### Distinguishing Effects of El Niño Southern Oscillation from Natural Short-term Climate Variability: A Case Study

Mark A. Rose\
Meteorologist\
National Weather Service\
Nashville, Tennessee

\- and -

Darrell R. Massie\
Senior Meteorologist\
National Weather Service\
Nashville, Tennessee

**ABSTRACT**

There are some regions of the United States where a general unambiguous
correlation has been documented between ENSO warm and cold episodes and
the departure from normal of average winter temperature and
precipitation. There are other regions, however, where the signal is
more ambiguous or seemingly impossible to define. The question that
often arises during ENSO climate studies is, \"How can a climate effect
caused by ENSO be distinguished from natural short-term climate
variability?\" In regions where the correlation is strong and
unambiguous, this question can often be deferred. However, in regions
where former research has indicated ambiguous correlations, this
question becomes a paramount concern. Perhaps, if we can find a way to
distinguish between particular climate trends that are occurring
simultaneously, we will be able to more completely analyze "ambiguous
regions.\" In doing so, a determination can hopefully be made as to
whether ENSO anomalies exist or if ENSO actually enhances other ongoing
climate trends. Previous studies have shown that Nashville, Tennessee,
falls into a region of the United States where the effects from ENSO are
ambiguous. However, this study will show that when ENSO is considered in
context with other natural short-term climate variability of longer
periodicity, there is a great deal of evidence linking ENSO with
particular climatic impacts at Nashville \-- sometimes occurring as a
climate anomaly and sometimes seeming to enhance other ongoing
short-term climate trends.

This study will show the inadequacy of regional ENSO studies that do not
give proper weight to the effects of natural short-term climate
variability. It will show that even in regions heretofore known to
exhibit ambiguous effects from ENSO, natural short-term climate
variability likely plays a major role in determining the type of weather
a particular ENSO event will produce \-- something that would be missed
if simple correlations were the only focus of the study. It will be
shown that the climatologically unique period of the late 1950\'s and
1960\'s tended to produce particular types of weather at Nashville
during El Niño and La Niña. Some of the effects were positively
correlated with the short-term climate variability, whereas other
effects were anomalous. Certain unique climate signals were also found
in the data that might help forecasters make general weather predictions
for upcoming months, and even entire seasons. Findings suggest that El
Niño drying trends, as well as unusually warm La Niña weather, can
likely be predicted for Nashville by closely observing local trends in
the weather during the summer and fall months leading into an ENSO
event.

**1. Introduction**

Climatologists and meteorologists have conducted numerous studies to
look for correlations between ENSO warm and cold episodes and certain
seasonal climate conditions. This is usually done by studying
meteorological records during ENSO events in order to reveal anomalous
deviations in prevailing weather patterns that might be attributable to
the El Niño Southern Oscillation. However, due to the complexities of
climate variability it is often debatable whether a certain fluctuation
can be easily attributed to any particular source. Possible correlations
can be tested for statistical significance, and statistical significance
can be used to assess the confidence in a particular relationship. There
are other times, however, when a climate signal related to ENSO appears
highly ambiguous (i.e., no correlation with a reasonably high degree of
significance can be established). These are the times when strict
attention must be given to investigative methodology so that the climate
variable of interest (in this case, effects from ENSO) can be
effectively isolated from other natural short-term variability.

As prior research has shown, the climate for a particular spot or region
often tends to change in cyclical fashion over varying periods of time.
Thus, it is reasonable to believe that the type of weather defined as
\"average\" or \"anomalous,\" changes as well. However, defining natural
patterns and trends can be a tricky matter because ultimately it
involves the introduction of a certain degree of subjectivity. For
instance, to investigate climate trends, one can choose from a variety
of methods and time frames. Trigonometric best-fit polynomials can be
used to approximate the data or, perhaps, running means can be used for
the same purpose. A ten-year data set might be used or, perhaps, a
100-year data set may be desired. Different trends may appear in the
data, depending upon which method and time frame are chosen. However, to
ignore the important implications of such trends to an ENSO climate
study such as this, can be detrimental to the degree of scientific
confidence one can place in the conclusions. After all, if no attempt is
made to define natural short-term climate variability present in the
climate record *not* attributable to El Niño, how can the significance
of climate correlations associated *with* El Niño be fully understood or
thoroughly defined? To help clarify the impact of short-term climate
variability on the effect of [ENSO]{.underline}, a new series of
web-based graphics has been provided by the Climate Prediction Center
(CPC) that shows three-month average temperature and precipitation for
the United States for the previous ten years. As such, these graphics,
over time, will act as a moving short-term climate window, allowing us
to see real-time changes between short-term ENSO (ten-year) climate
averages and averages for the entire ENSO record.

Previous local studies at the National Weather Service in Nashville
attempted to find correlation(s) between ENSO events and certain
prevailing weather conditions. However, these studies were inconclusive
(i.e., no correlations could be clearly established). This particular
study differs from previous ones because the methodology includes a
mechanism for placing Nashville weather experienced during ENSO events
in context with the ongoing short-term climate trends, and also
considers changes in the 30-year climatological averages ([Appendix
5](http://www.srh.noaa.gov/ohx/research/el_nino/appendix5.htm)). These
factors are considered so their contribution to the average weather
conditions can be eliminated, thus allowing any possible ENSO-related
anomalies to be more easily revealed. The overall methodology
established to perform this task is called a \"climate filter\" and is
defined in great detail in the succeeding text.

**2. What is El Niño?**

El Niño is generally defined as a warm temperature anomaly of the
eastern Pacific Ocean. During this anomaly, the physical relationships
between wind, ocean currents, and ocean and air temperatures create a
pattern that has a significant impact on the weather around the world
(NASA, 2006).

South Americans who fish the waters off the coast of Peru and Ecuador
have known about El Niño for centuries. Every three to seven years
during the months of December and January, fish in these coastal waters
nearly vanish. Fishermen have given this phenomenon the name El Niño,
which is Spanish for \"the boy child\" because it occurs around the time
of the celebration of the birth of the Christ child.

The development of El Niño has its origins in the western Pacific Ocean
(NWS, 2006). Easterly trade winds diminish and a westerly anomaly
develops. As a result, warming of the surface layers in the eastern and
central equatorial Pacific Ocean occurs.

El Niño events occur irregularly at intervals of 2 to 7 years, although
the average is about once every 3 to 4 years. They typically last 12 to
18 months, and are accompanied by the \"Southern Oscillation\" \-- an
inter-annual seesaw in tropical sea-level pressure between the eastern
and western hemispheres. (During the 54-year period of study contained
in this paper, there were 14 El Niño events, an average of one every 3.9
years. The average duration was 13 months.)

During El Niño, unusually high atmospheric sea-level pressures typically
develop in the western tropical Pacific and Indian Ocean regions, and
unusually low sea-level pressures develop in the southeastern tropical
Pacific. This pattern contributes to a shift in mid-latitude synoptic
weather patterns. Southern Oscillation tendencies for unusually low
pressures west of the date line and high pressures east of the date line
have also been linked to periods of anomalously cold equatorial Pacific
sea surface temperatures (SST\'s), sometimes referred to as \"La Niña.
\"

The Climate Prediction Center notes that \"During a warm episode winter,
mid-latitude low pressure systems tend to be more vigorous than normal
in the region of the Gulf of Alaska. These systems pump abnormally warm
air into western Canada, Alaska, and the extreme northern portion of the
contiguous United States. Storms also tend to be more vigorous in the
Gulf of Mexico and along the southeast coast of the United States
resulting in wetter than normal conditions in that region.\"

![](media/image1.wmf){width="5.34375in" height="2.8333333333333335in"}

For historical purposes, according to NCEP, cold and warm episodes are
defined when sea surface temperatures in the El Niño region differ from
the climatological normal by at least 0.5^o^C, and exist for a minimum
of five consecutive overlapping three-month periods (NCEP, 2006).

Figure 1 shows sea surface temperature anomalies of at least \|0.5^o^C\|
which indicate all El Niño and La Niña events used in this study. (The
zero line represents the climatological normal for the 1971-2000\* base
period.) Also note that the data used in this study are for El Niño
region 3.4, which lies between 120^o^W and 170^o^W, and between 5^o^N
and 5^o^S (Figure 2a).

![](media/image2.png){width="5.958333333333333in"
height="2.6145833333333335in"}

Figure 2a. ENSO SST regions. Adapted from NCEP (2007).

![](media/image3.png){width="5.0625in" height="2.4375in"}

Figure 2b. SST anomalies of at least \|0.5^o^C\| during the La Niña of
2007. Adapted from NCEP (2007).

\* NCEP applied the 1971-2000 climatological normals to the entire El
Niño period of record used in this study. This is statistically possible
because, according to Xue et al (2003), "The interdecadal changes in
Niño-3 (5^o^S--5^o^N, 90^o^--150^o^W) are small (0.2^o^)...."

**3. Other Research on the El Niño Southern Oscillation**

This is not the first research paper written on the effects of El Niño
at a particular location. A study by Lussky and Rieck (1997) analyzed
departures from normal during several ENSO winters, but did not place
these statistics in the larger context of the prevailing climatological
pattern. A similar study by Deedler (1997) presented departures from
normal during three ENSO winters, but, again, did not place these
statistics in the larger context of the prevailing climatological
pattern.

On a different note, Nunn and DaGaetano (2004) authored a paper on the
El Niño−Southern Oscillation and its role in cold-season tornado
outbreaks, but only considered climate data for November through
February.

**4. Methodology**

[Section I. Revisiting the case for ambiguous correlations between ENSO
and Nashville weather]{.underline}

As already stated, earlier published studies have shown Nashville to be
located in a region of the United States where the effects from ENSO are
ambiguous. In addition, earlier unpublished studies conducted at the
National Weather Service Forecast Office in Nashville, using local
weather data, verified this same general assertion. However, for the
purposes of this study, it is important to analyze the data again using
a specially-designed "climate filter" in order to either verify these
generalizations or present new findings.

As stated earlier, the Climate Prediction Center (CPC) tracks changes in
sea surface temperature departures from normal in the Niño 3.4 region
(5^o^N-5^o^S, 120^o^-170^o^W). This information is then used to compute
the Oceanic Niño Index (ONI). The ONI reflects a three-month composite
average, and changes in the index are tracked using running means. To
define a warm (El Niño) or cold (La Niña) episode there must be at least
5 consecutive periods when the ONI equals or exceeds the threshold of
+/- 0.5^o^.

Statistics provided by CPC show that the cold and warm episodes between
1950 and 2003 consisted of 347 cases when the ONI equaled or exceeded
+/-0.5^o^. Out of this set, there were 157 cases when ONI equaled or
exceeded +/-1.0^o^, 61 cases when ONI equaled or exceeded +/-1.5^o^, and
15 cases when the index equaled or exceeded +/-2.0^o^.

The average temperature and average precipitation at Nashville were
calculated for each three-month period that CPC used to define the
various warm and cold episodes. These data were then segregated based on
the nature of the episode (warm or cold), and used to search for
possible correlation with anomalies in Nashville\'s weather. They were
also used to determine whether any possible weather anomalies in
Nashville tended to increase or decrease with changes in SST intensity.

Realizing that 30-year averages show significant fluctuation over time,
departures from normal for precipitation and temperature were always
calculated using the base average pertinent for each of the 347
three-month periods. Normal values for the 1921-1950 period were used
for ENSO occurrences during the 1950\'s, normal values for the 1951-1980
period were used for ENSO occurrences during the 1980\'s, etc.

[Section II. Distinguishing effects of ENSO from natural short-term
climate variability]{.underline}

For each ENSO event, attempts were made to find any anomalies in the
temperature and precipitation data for Nashville that could conceivably
be attributed to El Niño and La Niña. This was done by considering the
data in context with the prevailing short-term climate and the
short-term climate trend ongoing at the time of the ENSO event. Weather
was defined as \"anomalous\" only when the data showed a departure from
*both* the prevailing short-term climate and the short-term climate
trend. This was done to try and \"filter out\" climate data that may
have been influenced by other natural short-term climate fluctuations.
In the following sections this derived process will be referred to
simply as a \"climate filter.\"

Smoothing of the data was achieved by calculating three-period running
means (TPM) using the three-month temperature and precipitation
departures from normal as the base data for each ENSO event. An example,
taken from Table 19 (Appendix 2), showing temperature data for La Niña
1954-1957, is shown below.

![](media/image4.png){width="4.072222222222222in"
height="1.6666666666666667in"}TPM (1954, AMJ) is the three-period
running mean calculated by adding the departures from normal that
occurred during periods \"1954, MAM\" (-0.4), \"1954, AMJ\" (0.4), and
\"1954, MJJ\" (0.0), and dividing by three. Thus, the three-period
running mean for TPM (1954, AMJ) is 0.0. The succeeding four values for
TPM in Table 19 are:

TPM (1954, MJJ) = 1.1

TPM (1954, JJA) = 2.2

TPM (1954, JAS) = 3.0

TPM (1954, ASO) = 2.2

This additional smoothing of data made it easier to distinguish climate
cycles. Once the smoothing was completed, a search was made to locate
the first inflection point *prior* to the ENSO maximum. An inflection
point is defined as the point where an established trend first begins to
change direction, even if that change only persists for one or two
three-month periods. This would indicate a point in the data where the
TPM changed from \"decreasing\" to \"increasing,\" or vice versa. [A
trend of \"decreasing\" to \"steady,\" or \"increasing\" to \"steady\"
was considered insufficient criteria for defining an inflection
point]{.underline}, where:

> "Decreasing" is associated with a negative value for the following
> equation, as we incrementally step our way back in time from the ENSO
> Max to earlier periods of the ENSO:
>
> T~ENSO\ Max\ -\ n~ -- T~ENSO\ Max\ --\ n+1~ (from n=0 to
> n=n~T-final~),
>
> Where n~T-final~ indicates the point in the TPM data, during the ENSO
> event, where either an inflection point was observed or the beginning
> point of the ENSO was reached (i.e., no inflection point was found).

"Increasing" is associated with a positive value from the above
equation.

"Steady" is associated with a value of zero from the above equation.

The trend must have shown clear signs of reversal before it was defined
as an inflection. No importance was attributed to the magnitude of the
inflection. Thus, an inflection might indicate a relatively brief, minor
interruption in a trend, or a relatively long, significant change in the
trend. The important thing was to locate the point where a \"new\" trend
first became clearly established that would persist until the time of
the ENSO maximum. If an inflection point was found, the pattern length
(PL) was defined as twice the length of time between the inflection
point and the ENSO maximum. The pattern length always included an equal
period of time before and after the ENSO maximum. This was done so that
the period would be centered on the ENSO maximum itself, and would allow
for analysis of a \"post-ENSO Max\" period where weather conditions at
Nashville could conceivably still be influenced by a waning ENSO. When
such cycles appeared in the data, the pattern length was noted and an
average PL (PL~avg~) was later calculated for the warm episode data set
(154 cases) and the cold episode data set (193 cases). The calculation
of PL~avg~ was done in order to see if it might be utilized in the
future as part of a general forecast scheme. For instance, if a
correlation is found between a certain type of climate trend and a
certain type of ENSO event (i.e., \"warm\" or \"cold\"), it would be
theoretically possible to utilize the characteristics of a developing
ENSO, along with PL~avg~ and a chart of running means for the developing
ENSO event to reveal the initial stages of an ENSO-related climate
trend.

It was assumed that if an inflection point could be found in the data
during the early stages of an ENSO event, indicating the beginning of a
temperature or precipitation trend, there would be an increased chance
that a correlation might exist between Nashville weather and the
presence of an ENSO event. Figure 3 shows a portion of the temperature
trend analysis of the El Niño of AMJ 1982 to MJJ 1983:

![](media/image5.png){width="6.457638888888889in"
height="4.457638888888889in"}

The values for PL~avg~, for both the precipitation and temperature data,
were then used to define a \"climatologically significant period\" for
each El Niño and La Niña event. In other words, PL~avg~, for all intents
and purposes, indicates the short-term period during which Nashville
weather most often appeared to establish ENSO-related trends. It should
be noted that there were some data sets where an inflection point could
not be found. These were times when the early part of the ENSO event was
either too brief to allow for determination of an inflection point
(i.e., El Niño 1969-1970, temperature data), or a trend was found but no
inflection point was observed (i.e., El Niño 1965-1966, temperature
data). (Refer to TPM columns and Appendix 4.) The pertinent TPM data for
El Niño 1969-1970 and El Niño 1965-1966 are provided in the examples
below:

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Excerpt                                                                                                                            
  from Table 9.                                                                                                                        
  El Niño                                                                                                                              
  1969-1970**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1969          ASO          0.6         69.8            71.1        -1.3           **TPM**   6.34              8.05        0.79       **TPM**

  1969          SON          0.7         59.3            60.9        -1.6           -1.8      5.90              8.47        0.70       0.70

  1969          OND          0.7         48.1            50.5        -2.4           -2.9      11.87             9.79        1.21       0.92

  1969          NDJ          0.6         38.6            43.2        -4.6           -4.1      11.02             12.96       0.85       1.00

  1970          DJF          0.5         35.9            41.1        -5.2                     13.55             14.19       0.95        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

Notice here that the SST maximum anomaly occurred very close to the
beginning of the El Niño (SON, 1969). There was insufficient pre-ENSO
Max TPM data to show an inflection point.

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Excerpt                                                                                                                            
  from Table 7.                                                                                                                        
  El Niño                                                                                                                              
  1965-1966**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1965          MJJ          0.6         75.1            75.4        -0.3           **TPM**   9.18              10.69       0.86       **TPM**

  1965          JJA          1.0         77.6            79.0        -1.4           -0.7      8.59              9.83        0.87       0.96

  1965          JAS          1.2         77.2            77.5        -0.3           -0.7      10.87             9.45        1.15       1.01\*

  1965          ASO          1.4         70.7            71.1        -0.4           0.0       8.12              8.05        1.01       1.01\*

  1965          SON          1.5         61.7            60.9        0.8            0.6       7.41              8.47        0.87       0.74

  1965          OND          1.6         52.0            50.5        1.5            0.7       3.40              9.79        0.35       0.58

  1965          NDJ          1.5         42.9            43.2        -0.3           -0.2      6.76              12.96       0.52       0.49

  1966          DJF          1.2         39.4            41.1        -1.7           -1.5      8.57              14.19       0.60       0.57

  1966          JFM          1.1         41.3            43.7        -2.4           -1.4      8.95              15.19       0.59       0.65

  1966          FMA          0.8         50.3            50.4        -0.1           -1.2      10.10             13.44       0.75       0.72

  1966          MAM          0.5         58.1            59.1        -1.0                     10.46             12.65       0.83        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

Notice here that the SST Maximum anomaly occurred deep in the ENSO event
(OND, 1965) However, the pre-ENSO Max trend was \"decreasing,\" then
\"steady,\" which does not provide sufficient evidence of an inflection
point using our established criteria.

To define natural short-term climate trends that existed, separate and
apart from ENSO, a classification methodology had to be established. An
objective definition for \"prevailing short-term climate\" and
\"short-term climate trend\" was established to characterize the general
short-term climate at Nashville. A subjective decision was made to use
the length of time for a short-term trend as five years, centered on the
year of the ENSO maximum. An explanation of this methodology is detailed
in [Appendix
3](http://www.srh.noaa.gov/ohx/research/el_nino/appendix3.htm). The
short-term climate definitions were characterized as follows:

FOR TEMPERATURE DATA:

[Characteristics for prevailing short-term climate (El
Niño)]{.underline}\
**Near normal:** departure from normal of 0.8^o^ to -0.8^o^\
**Cool:** departure from normal of -0.9^o^ to -1.7^o^\
**Very Cool:** departure from normal greater than -1.7^o^\
**Warm:** departure from normal of 0.9^o^ to 1.7^o^\
**Very Warm:** departure from normal greater than 1.7^o^

[Characteristics for prevailing short-term climate (La
Niña)]{.underline}\
**Near normal:** departure from normal of 0.6^o^ to -0.6^o^\
**Cool:** departure from normal of -0.7^o^ to -1.2^o^\
**Very Cool:** departure from normal greater than -1.2^o^\
**Warm:** departure from normal of 0.7^o^ to 1.2^o^\
**Very Warm:** departure from normal greater than 1.2^o^

[Characteristics for short-term climate trend (El Niño)]{.underline}\
**Stable:** a change of 0.8^o^ to -0.8^o^\
**Cooling:** a change of -0.9^o^ to -1.7^o^\
**Significant Cooling:** a change greater than -1.7^o^\
**Warming:** a change of 0.9^o^ to 1.7^o^\
**Significant Warming:** a change greater than 1.7^o^

[Characteristics for short-term climate trend (La Niña)]{.underline}\
**Stable:** a change of 0.6^o^ to -0.6^o^\
**Cooling:** a change of -0.7^o^ to -1.2^o^\
**Significant Cooling:** a change greater than -1.2^o^\
**Warming:** a change of 0.7^o^ to 1.2^o^\
**Significant Warming:** a change greater than 1.2^o^

FOR PRECIPITATION DATA:

[Characteristics for prevailing short-term climate (El
Niño)]{.underline}\
**Near normal:** departure from normal of 7% to -7%\
**Dry:** departure from normal of -8% to -15%\
**Very Dry:** departure from normal greater than -15%\
**Wet:** departure from normal of 8% to 15%\
**Very Wet:** departure from normal greater than 15%

[Characteristics for prevailing short-term climate (La
Niña)]{.underline}\
**Near normal:** departure from normal of 8% to -8%\
**Dry:** departure from normal of -9% to -17%\
**Very Dry:** departure from normal greater than -17%\
**Wet:** departure from normal of 9% to 17%\
**Very Wet:** departure from normal greater than 17%

[Characteristics for short-term climate trend (El Niño)]{.underline}\
**Stable:** a change of 7% to -7%\
**Decreasing:** a change of -8% to -15%\
**Rapidly Decreasing:** a change greater than -15%\
**Increasing:** a change of 8% to 15%\
**Rapidly Increasing:** a change greater than 15%

[Characteristics for short-term climate trend (La Niña)]{.underline}\
**Stable:** a change of 8% to -8%\
**Decreasing:** a change of -9% to -17%\
**Rapidly Decreasing:** a change greater than -17%\
**Increasing:** a change of 9% to 17%\
**Rapidly Increasing:** a change greater than 17%

An explanation of why these particular thresholds were chosen is
outlined in [Appendix
3](http://www.srh.noaa.gov/ohx/research/el_nino/appendix3.htm).

Below is an example showing the El Niño of AMJ 1982 to MJJ 1983, and its
relative position in the short-term temperature trend and prevailing
short-term climate.

![](media/image6.png){width="6.457638888888889in"
height="4.322222222222222in"}

SHORT-TERM CLIMATE TREND = \[Running mean for 1984\] - \[Running mean
for 1980\] / 5 yrs

          = (59.0 - 58.3) / 5 yrs

          = +0.7^o^ / 5 yrs

          = \"Stable\" (See list above for definition.)

PREVAILING SHORT-TERM CLIMATE = \[Running mean for 1982, year of ENSO
Max\] - \[30-yr avg\]

          = 58.5 - 59.2

          = -0.7^o^

          = \"Near normal\" (See list above for definition.)

As shown in Table 3a and Figure 3b, the average temperature departure
from normal experienced during El Niño 1982-1983 was 2.7^o^ (i.e., "very
warm"). Thus, this El Niño exhibited anomalous weather because neither
of the short-term climate signals was in phase with this particular type
of weather. In other words, the weather during that particular El Niño
can be convincingly distinguished from the two short-term climate
signals. This same type of analysis was conducted on all other ENSO
events and the results are provided in Tables 3a and 3b.

**5. Results**

In Section I, there are 347 three-month ONI values considered for
possible correlation with SST anomaly strength. Since this number is
well above the 30 normally considered as a threshold for significance
testing, we are able to comment regarding the statistical significance
of various suspected correlations. However, for the remainder of this
study, the data sets under investigation will typically be much smaller.
For instance, when El Niño and La Niña subsets are considered, there are
only 16 and 15 cases, respectively. Thus, statistical significance will
remain a largely unsettled question. However, the number of documented
ENSO events is not something we can alter. We can only study and draw
conclusions from the data that nature has provided up to the present.
Thus, the statistical significance of the various correlations found in
this study will, to a certain extent, remain open for debate until more
data becomes available from future ENSO events.

[Section I. Searching for climate anomalies at Nashville, *without*
using a climate filter]{.underline}

Table 1 (below) provides a general summary of climate statistics for
Nashville, Tennessee, during El Niño and La Niña patterns between 1950
and 2003. Statistics accumulated for all events are included on the
first line of the table, for SST anomaly ≥0.5^o^C. Each succeeding line
includes statistics for increasingly smaller subsets of data for ENSO
events exhibiting increasingly large SST anomalies.

  --------------- ----------- --------------- --------------- ----------- --------------- ---------------
  **Table 1.                                                                              
  Temperature and                                                                         
  Precipitation                                                                           
  Departures from                                                                         
  Normal at                                                                               
  Nashville,                                                                              
  Tennessee,                                                                              
  during El                                                                               
  Niño/La Niña                                                                            
  Patterns                                                                                
  (1950-2003)**                                                                           

  **SST\          **El Niño**                                 **La Niña**                 
  Anomaly                                                                                 
  (^o^C)**                                                                                

                  **Cases**   **Temperature   **Ratio of      **Cases**   **Temperature   **Ratio of
                              Departure from  Observed                    Departure from  Observed
                              Normal (^o^F)** Precipitation               Normal (^o^F)** Precipitation
                                              to Normal**                                 to Normal**

  **≥0.5**        154         -0.5            1.02            193         0.3             1.04

  **≥1.0**        76          0.0             0.96            81          1.1             1.03

  **≥1.5**        35          0.5             0.95            26          2.3             1.24

  **≥2.0**        13          1.5             1.10            2           1.1             1.16
  --------------- ----------- --------------- --------------- ----------- --------------- ---------------

1\. With respect to El Niño events, temperatures at Nashville show an
overall departure from normal of 0.5^o^ or less for all SST anomalies,
except those SST anomalies that are 2.0^o^ or more. Here, the average
observed temperature at Nashville was 1.5^o^ above normal. But with only
13 cases falling into this subcategory, the statistical sample is too
small to make a definitive conclusion. (Here, \"n=30\" represents the
minimum threshold for statistical significance.) The results are,
therefore, somewhat ambiguous.

2\. La Niña events are associated with the greatest departure from
normal temperatures at Nashville. In all subcategories where the SST
anomaly was at least 1.0^o^, the observed temperature averaged 1.1^o^ or
more above normal. Here, the sample size (n=81) is sufficiently large to
suggest a certain degree of confidence in a possible correlation between
La Niña and warmer-than-normal temperatures at Nashville. However, that
the greatest temperature departure of 2.3^o^ occurs with SST anomalies
in the range of 1.5^o^ to 1.9^o^, rather than 2.0^o^+, makes it
impossible to establish a definitive correlation between increasing ENSO
intensity and increasing warmth.

3\. As for observed precipitation, El Niño again coincided with
relatively small departures from normal. When SST anomalies were at
least one-half degree, but less than 2.0^o^, precipitation ranged from
2% above normal to 5% below. When SST anomalies were ≥2.0^o^, observed
precipitation was 10% above normal, but, again, the sample size is too
small to make a definitive conclusion (i.e., results are, once again,
somewhat ambiguous).

4\. La Niña shows larger deviations from normal than El Niño with regard
to precipitation, just as it did for temperature; although this applies
only when SST anomalies reach at least 1.5^o^. Here, there were 28
cases, with the observed precipitation running 16-24% above normal.
However, again using \"n=30\" as a minimum threshold for significance,
the sample size is too small to make definitive conclusions. Again, the
results are somewhat ambiguous.

Of the four data subsets analyzed, only one showed any indication of
being unambiguous \-- the one for average temperature during La Niña
events. The remaining three parameter subsets failed to show any
evidence of a clear correlation with either a particular ENSO pattern
type or the strength of the pattern. There was a hint, however, that
increasing strength of La Niña might be associated with increased
positive departures from normal of both temperature and precipitation
(especially when the SST anomaly is ≥1.0^o^).

[Section II. Searching for climate anomalies at Nashville through
application of a \"climate filter\"]{.underline}

![](media/image7.png){width="3.99375in" height="2.2895833333333333in"}A
brief set of statistical conclusions, as just provided in Section I, may
not be the best way to define possible impacts of El Niño and La Niña on
Nashville\'s climate \-- especially when considering the ambiguous
nature of most of the results. As discussed earlier, a more rigorous
method should be applied, where individual El Niño/La Niña occurrences
are studied in context with other natural short-term climate trends.
Consider, for example, an ENSO occurrence that is associated with warm
and dry conditions at Nashville. If the ENSO happens to be embedded in
an overall short-term climate pattern that is warmer and drier than
normal, then it becomes more difficult to suggest with confidence that
the ENSO occurrence had a significant impact on the observed weather. On
the other hand, if an ENSO occurrence is associated with a significant
departure from the prevailing short-term climate and short-term climate
trend, then a stronger case can be made that the ENSO may have impacted
the observed weather. (This will be the focus of Section 6.)

To establish a method for defining the \"prevailing short-term\" climate
and the \"short-term climate trend\" at Nashville during each ENSO
event, Nashville climate data were smoothed by calculating five-year
running means. This was done so that cycles and trends could be more
easily observed. Figures 4a and 4c show Nashville\'s average annual
temperature and precipitation, respectively. Figures 4b and 4d show
plots of the running means. The origin for the graphs has been chosen to
be 1945 in order that the prevailing trends leading into the period of
study could be shown. A comparison of the graphs of the observed data
and the running means clearly shows how the \"noise\" from random
variability in the observed data has been minimized and general trends
and cycles have become more obvious.

![](media/image9.png){width="3.99375in"
height="2.2895833333333333in"}Figures 4a through 4d include dashed
horizontal lines representing the normal temperature at Nashville during
the applicable 30-year base period. The light gray overlay on each
figure is the same sea surface temperature anomaly plot shown in Figure
1 which indicates the El Niño/La Niña periods.

As stated earlier, in the section on research methodology, attempts were
made to find a value for PL~avg~ for the El Niño and La Niña data sets.
This value was used to represent the average period during \"warm\" and
\"cold\" episodes during which Nashville weather most often appeared to
establish ENSO-related trends. The value for PL~avg~ was calculated
using the unique PL value for each ENSO event, where

PL = \[2 x N~pre-SST\ Max\ periods~\] + 1,

where N~pre-SST\ Max\ periods~ indicates the number of periods between
the SST Max anomaly and the pre-SST Max inflection point (indicated in
the maximally smoothed temperature and precipitation data). As stated
earlier, some ENSO events did not exhibit an inflection point and could
not be considered when calculating PL~avg~.

![](media/image10.png){width="3.99375in"
height="2.2895833333333333in"}The base data used for calculating PL~avg~
are provided in Tables 34 and 35 in [Appendix
4](http://www.srh.noaa.gov/ohx/research/el_nino/appendix4.htm). The
PL~avg~ for El Niño events, for both temperature data and precipitation
data, was found to be 5. The PL~avg~ for La Niña events, for both
temperature data and precipitation data, was also 5.

Table 34, in [Appendix
4](http://www.srh.noaa.gov/ohx/research/el_nino/appendix4.htm), shows
that during the ten El Niño events where an inflection point could be
found in the \"pre-SST Max\" precipitation trend, the inflection was
always characterized as a relative maximum. This was deemed significant.
Therefore, an investigation was conducted to more completely define this
pre-SST Max in the precipitation data.

The data in Table 2a show that the months of September and/or October
had a high frequency of occurrence in the running means composite period
at the place where the maximum tended to occur (located at \"ENSO Max -
2\" periods). This occurred 90% of the time in this subset of ten cases.
October was represented in 100% of these cases and September was
represented in 67%. When extending the subset to include cases where the
ENSO record of smoothed data failed to extend past \"ENSO Max - 1\" and
cases where length of the pre-SST Max period met criteria but failed to
exhibit an inflection point, the subset size increased to 14. The
percentage of these cases where September and/or October showed up in
the running means composite \"max\" period was 86%. October was
represented in 86% of the cases and September was represented in 64%.

When using the expanded subset of 14 El Niños, where the pre-SST Max
ENSO record was extended to include the \"ENSO Max - 1,\" we find that
when September was part of the three-month running mean composite, 89%
of those Septembers showed above-normal precipitation (Table 2b). When
October was part of the three-month running mean composites, 69% of
those Octobers showed above-normal precipitation (Table 2b). More
importantly, in this subset of 14 cases, either September or October (or
both) had above-normal precipitation 79% of the time. The only two El
Niños that failed to meet criteria for consideration in this part of the
study were those in 1969-1970 and 1993. Each of these El Niños reached a
maximum anomaly too early in the ENSO for consideration.

The average ratio of total precipitation to normal precipitation for all
\"pre-SST Max periods\" (located at \"ENSO Max -- 2\" or \"ENSO Max --
1\") was 1.23, indicating average precipitation that was 23% above
normal. Using our previously defined thresholds, based on standard
deviation, this would be defined as "very wet."

  --------------- -------- ------------------------------------ ------------------
  **Table 2a.                                                   
  Months included                                               
  in the pre-ENSO                                               
  Max inflection                                                
  point for El                                                  
  Niño                                                          
  precipitation                                                 
  data (using the                                               
  maximally                                                     
  smoothed data                                                 
  set)**                                                        

  **Event**       **ENSO   **Pre-SST Max period (located at     **Ratio of total
                  Max**    \"ENSO Max - 2\" or \"ENSO Max -     to normal (TPM)**
                           1\")**                               

  1957-58\*       DJF      OND                                  1.48

  1963-64         OND      ASO                                  1.26

  1965-66\*       OND      ASO                                  1.01

  1968-69         DJF      OND                                  1.10

  1969-70         SON      \-\--                                \-\--

  1972-73\*       NDJ      SON                                  1.55

  1976-77         OND      ASO                                  1.44

  1977-78         OND      ASO                                  1.61

  1982-83\*       NDJ      SON                                  0.97

  1986-88 (1)\*   DJF      OND                                  1.13

  1986-88 (2)\*   JAS      MJJ                                  0.67

  1991-92\*       DJF      OND                                  1.17

  1993            MAM      \-\--                                \-\--

  1994-95\*       NDJ      SON                                  1.11

  1997-98\*       OND      ASO                                  1.30

  2002-03\*       OND      ASO                                  1.41
  --------------- -------- ------------------------------------ ------------------

\* indicates an El Niño event where a pre-SST Max inflection point could
be found (as shown in table 34).

\-\-- indicates that the El Niño event \"maxed out\" early in the event
and prevented the consideration of a period located at \"ENSO Max - 2\"
or "ENSO Max -- 1."

  ----------- ---------------------- ------------ -------------------- ------------
  **Table 2b.                                                          
  October and                                                          
  September                                                            
  rainfall                                                             
  during                                                               
  pre-ENSO                                                             
  Max                                                                  
  periods\                                                             
  (located at                                                          
  \"ENSO Max                                                           
  -- 2\" or                                                            
  \"ENSO Max                                                           
  -- 1\")**                                                            

  **Year**    **Observed September   **Computed   **Observed October   **Computed
              rainfall/normal        ratio**      rainfall/normal      ratio**
              September rainfall**                October rainfall**   

  1957\*      \-\--/\-\--            \-\--        3.89/2.52            1.54

  1963        3.43/3.59              0.96         T/2.32               0.00

  1965\*      5.02/3.59              1.40         0.57/2.32            0.25

  1968        \-\--/\-\--            \-\--        3.92/2.32            1.69

  1972\*      3.71/3.42              1.08         4.06/2.16            1.88

  1976        5.08/3.42              1.49         5.17/2.16            2.39

  1977        5.04/3.42              1.47         4.22/2.16            1.95

  1982\*      3.23/2.74              1.18         1.91/2.58            0.74

  1986(1)\*   \-\--/\-\--            \-\--        2.19/2.58            0.85

  1986(2)\*   \-\--/\-\--            \-\--        \-\--/\-\--          \-\--

  1991\*      \-\--/\-\--            \-\--        3.88/2.62            1.48

  1994        4.20/2.87              1.46         3.31/2.62            1.26

  1997        5.75/2.87              2.00         2.71/2.62            1.03

  2002        6.29/3.09              2.04         4.48/2.87            1.56
  ----------- ---------------------- ------------ -------------------- ------------

\* indicates that this particular ONI period also represented a pre-ENSO
Max period and an inflection point in the precipitation trend

\-\-- indicates that particular month was not part of the pre-ENSO Max
period

Notes: (1) The two El Niño events that \"maxed out\" early in the event
(1969-70 and 1993), and prevented the consideration of a period located
at ENSO Max - 2 are not included in this table. (2) "Normal rainfall"
refers to the normal for the preceding 30-year period (Appendix 5).

[Summary of ENSO events and their placement in the overall short-term
climate record at Nashville]{.underline}

The ENSO Nashville climate data were further summarized for inclusion in
Tables 3a and 3b in order to place each event in context with the
short-term climate at Nashville. The average observed departure from
normal for temperature and precipitation that occurred within the
boundaries of PL~avg~ was calculated (with base data for these
calculations noted by the green and red number sequences in the tables
in Appendices
[1](http://www.srh.noaa.gov/ohx/research/el_nino/appendix1.htm) &
[2](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm)). The
prevailing short-term climate and short-term climate trends were noted
for each El Niño/La Niña cycle and were based on a particular
methodology utilizing the five-year running mean temperature and annual
precipitation data. (See [Appendix
3](http://www.srh.noaa.gov/ohx/research/el_nino/appendix3.htm).)

There were some ENSO events when the maximum SST anomaly either occurred
at the onset of the event or so close to the beginning of the event that
the required number of \"pre-SST Max periods\" was not available for a
full five-period calculation. However, the calculations were still made
using a less-than-optimal number of periods and included in Tables 3a
and 3b. Such calculations are denoted with an asterisk (\*) in the
tables, along with the number of periods used in the calculations
(enclosed within parentheses).

Observed event departures were then compared with the prevailing climate
and climate trends to note whether each El Niño/La Niña cycle produced
general weather characteristics that differed from the short-term
climate and climate trend (i.e. were most likely anomalous).

+-----+----+------+------+------+------+------------+-------+-------+
| *   |    |      |      |      |      |            |       |       |
| *Ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 3a. |    |      |      |      |      |            |       |       |
| S   |    |      |      |      |      |            |       |       |
| umm |    |      |      |      |      |            |       |       |
| ary |    |      |      |      |      |            |       |       |
| of  |    |      |      |      |      |            |       |       |
| El  |    |      |      |      |      |            |       |       |
| N   |    |      |      |      |      |            |       |       |
| iño |    |      |      |      |      |            |       |       |
| O   |    |      |      |      |      |            |       |       |
| ccu |    |      |      |      |      |            |       |       |
| rre |    |      |      |      |      |            |       |       |
| nce |    |      |      |      |      |            |       |       |
| s** |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| **E | *  | **   | *    |      |      | **Pre      |       |       |
| ven | *P | Maxi | *Tem |      |      | cipitation |       |       |
| t** | er | mum\ | pera |      |      | Charact    |       |       |
|     | io | SST\ | ture |      |      | eristics** |       |       |
|     | ds | A    | C    |      |      |            |       |       |
|     | ** | noma | hara |      |      |            |       |       |
|     |    | ly** | cter |      |      |            |       |       |
|     |    |      | isti |      |      |            |       |       |
|     |    |      | cs** |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
|     |    |      | **   | *    | **   | **Ratio of | **    | *     |
|     |    |      | Aver | *Pre | ∆T** | observed   | Preva | *∆P** |
|     |    |      | age\ | vail |      | pre        | iling |       |
|     |    |      | o    | ing\ |      | cipitation | sh    |       |
|     |    |      | bser | sho  |      | to         | ort-\ |       |
|     |    |      | ved\ | rt-\ |      | normal**   | term  |       |
|     |    |      | de   | t    |      |            | clim  |       |
|     |    |      | part | erm\ |      |            | ate** |       |
|     |    |      | ure\ | c    |      |            |       |       |
|     |    |      | f    | lima |      |            |       |       |
|     |    |      | rom\ | te** |      |            |       |       |
|     |    |      | norm |      |      |            |       |       |
|     |    |      | al** |      |      |            |       |       |
|     |    |      |      |      |      |            |       |       |
|     |    |      | *    |      |      |            |       |       |
|     |    |      | *for |      |      |            |       |       |
|     |    |      | P    |      |      |            |       |       |
|     |    |      | L~av |      |      |            |       |       |
|     |    |      | g~** |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 15 | 1.6  | -3.8 | Near | Coo  | 1.01       | Near  | Incre |
| N   |    |      |      | no   | ling |            | n     | asing |
| iño |    |      |      | rmal |      |            | ormal |       |
| 19  |    |      |      |      |      |            |       |       |
| 57- |    |      |      |      |      |            |       |       |
| 195 |    |      |      |      |      |            |       |       |
| 8]( |    |      |      |      |      |            |       |       |
| htt |    |      |      |      |      |            |       |       |
| p:/ |    |      |      |      |      |            |       |       |
| /ww |    |      |      |      |      |            |       |       |
| w.s |    |      |      |      |      |            |       |       |
| rh. |    |      |      |      |      |            |       |       |
| noa |    |      |      |      |      |            |       |       |
| a.g |    |      |      |      |      |            |       |       |
| ov/ |    |      |      |      |      |            |       |       |
| ohx |    |      |      |      |      |            |       |       |
| /re |    |      |      |      |      |            |       |       |
| sea |    |      |      |      |      |            |       |       |
| rch |    |      |      |      |      |            |       |       |
| /el |    |      |      |      |      |            |       |       |
| _ni |    |      |      |      |      |            |       |       |
| no/ |    |      |      |      |      |            |       |       |
| app |    |      |      |      |      |            |       |       |
| end |    |      |      |      |      |            |       |       |
| ix1 |    |      |      |      |      |            |       |       |
| .ht |    |      |      |      |      |            |       |       |
| m#t |    |      |      |      |      |            |       |       |
| abl |    |      |      |      |      |            |       |       |
| e3) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 7  | 1.0  | -2.2 | Cool | St   | 0.76       | Near  | S     |
| N   |    |      |      |      | able |            | n     | table |
| iño |    |      |      |      |      |            | ormal |       |
| 19  |    |      |      |      |      |            |       |       |
| 63- |    |      |      |      |      |            |       |       |
| 196 |    |      |      |      |      |            |       |       |
| 4]( |    |      |      |      |      |            |       |       |
| htt |    |      |      |      |      |            |       |       |
| p:/ |    |      |      |      |      |            |       |       |
| /ww |    |      |      |      |      |            |       |       |
| w.s |    |      |      |      |      |            |       |       |
| rh. |    |      |      |      |      |            |       |       |
| noa |    |      |      |      |      |            |       |       |
| a.g |    |      |      |      |      |            |       |       |
| ov/ |    |      |      |      |      |            |       |       |
| ohx |    |      |      |      |      |            |       |       |
| /re |    |      |      |      |      |            |       |       |
| sea |    |      |      |      |      |            |       |       |
| rch |    |      |      |      |      |            |       |       |
| /el |    |      |      |      |      |            |       |       |
| _ni |    |      |      |      |      |            |       |       |
| no/ |    |      |      |      |      |            |       |       |
| app |    |      |      |      |      |            |       |       |
| end |    |      |      |      |      |            |       |       |
| ix1 |    |      |      |      |      |            |       |       |
| .ht |    |      |      |      |      |            |       |       |
| m#t |    |      |      |      |      |            |       |       |
| abl |    |      |      |      |      |            |       |       |
| e4) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 11 | 1.6  | 0.0  | Cool | St   | 0.67       | Near  | Decre |
| N   |    |      |      |      | able |            | n     | asing |
| iño |    |      |      |      |      |            | ormal |       |
| 19  |    |      |      |      |      |            |       |       |
| 65- |    |      |      |      |      |            |       |       |
| 196 |    |      |      |      |      |            |       |       |
| 6]( |    |      |      |      |      |            |       |       |
| htt |    |      |      |      |      |            |       |       |
| p:/ |    |      |      |      |      |            |       |       |
| /ww |    |      |      |      |      |            |       |       |
| w.s |    |      |      |      |      |            |       |       |
| rh. |    |      |      |      |      |            |       |       |
| noa |    |      |      |      |      |            |       |       |
| a.g |    |      |      |      |      |            |       |       |
| ov/ |    |      |      |      |      |            |       |       |
| ohx |    |      |      |      |      |            |       |       |
| /re |    |      |      |      |      |            |       |       |
| sea |    |      |      |      |      |            |       |       |
| rch |    |      |      |      |      |            |       |       |
| /el |    |      |      |      |      |            |       |       |
| _ni |    |      |      |      |      |            |       |       |
| no/ |    |      |      |      |      |            |       |       |
| app |    |      |      |      |      |            |       |       |
| end |    |      |      |      |      |            |       |       |
| ix1 |    |      |      |      |      |            |       |       |
| .ht |    |      |      |      |      |            |       |       |
| m#t |    |      |      |      |      |            |       |       |
| abl |    |      |      |      |      |            |       |       |
| e5) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 7  | 1.0  | -2.6 | Cool | St   | 1.00       | Near  | S     |
| N   |    |      |      |      | able |            | n     | table |
| iño |    |      |      |      |      |            | ormal |       |
| 19  |    |      |      |      |      |            |       |       |
| 68- |    |      |      |      |      |            |       |       |
| 196 |    |      |      |      |      |            |       |       |
| 9]( |    |      |      |      |      |            |       |       |
| htt |    |      |      |      |      |            |       |       |
| p:/ |    |      |      |      |      |            |       |       |
| /ww |    |      |      |      |      |            |       |       |
| w.s |    |      |      |      |      |            |       |       |
| rh. |    |      |      |      |      |            |       |       |
| noa |    |      |      |      |      |            |       |       |
| a.g |    |      |      |      |      |            |       |       |
| ov/ |    |      |      |      |      |            |       |       |
| ohx |    |      |      |      |      |            |       |       |
| /re |    |      |      |      |      |            |       |       |
| sea |    |      |      |      |      |            |       |       |
| rch |    |      |      |      |      |            |       |       |
| /el |    |      |      |      |      |            |       |       |
| _ni |    |      |      |      |      |            |       |       |
| no/ |    |      |      |      |      |            |       |       |
| app |    |      |      |      |      |            |       |       |
| end |    |      |      |      |      |            |       |       |
| ix1 |    |      |      |      |      |            |       |       |
| .ht |    |      |      |      |      |            |       |       |
| m#t |    |      |      |      |      |            |       |       |
| abl |    |      |      |      |      |            |       |       |
| e6) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 5  | 0.7  | -2.  | Cool | St   | 0          | Near  | S     |
| N   |    |      | 5^\* |      | able | .89^\*(4)^ | n     | table |
| iño |    |      | (4)^ |      |      |            | ormal |       |
| 19  |    |      |      |      |      |            |       |       |
| 69- |    |      |      |      |      |            |       |       |
| 197 |    |      |      |      |      |            |       |       |
| 0]( |    |      |      |      |      |            |       |       |
| htt |    |      |      |      |      |            |       |       |
| p:/ |    |      |      |      |      |            |       |       |
| /ww |    |      |      |      |      |            |       |       |
| w.s |    |      |      |      |      |            |       |       |
| rh. |    |      |      |      |      |            |       |       |
| noa |    |      |      |      |      |            |       |       |
| a.g |    |      |      |      |      |            |       |       |
| ov/ |    |      |      |      |      |            |       |       |
| ohx |    |      |      |      |      |            |       |       |
| /re |    |      |      |      |      |            |       |       |
| sea |    |      |      |      |      |            |       |       |
| rch |    |      |      |      |      |            |       |       |
| /el |    |      |      |      |      |            |       |       |
| _ni |    |      |      |      |      |            |       |       |
| no/ |    |      |      |      |      |            |       |       |
| app |    |      |      |      |      |            |       |       |
| end |    |      |      |      |      |            |       |       |
| ix1 |    |      |      |      |      |            |       |       |
| .ht |    |      |      |      |      |            |       |       |
| m#t |    |      |      |      |      |            |       |       |
| abl |    |      |      |      |      |            |       |       |
| e7) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 11 | 2.1  | 0.7  | Near | War  | 1.37       | Near  | Ra    |
| N   |    |      |      | no   | ming |            | n     | pidly |
| iño |    |      |      | rmal |      |            | ormal | incre |
| 19  |    |      |      |      |      |            |       | asing |
| 72- |    |      |      |      |      |            |       |       |
| 197 |    |      |      |      |      |            |       |       |
| 3]( |    |      |      |      |      |            |       |       |
| htt |    |      |      |      |      |            |       |       |
| p:/ |    |      |      |      |      |            |       |       |
| /ww |    |      |      |      |      |            |       |       |
| w.s |    |      |      |      |      |            |       |       |
| rh. |    |      |      |      |      |            |       |       |
| noa |    |      |      |      |      |            |       |       |
| a.g |    |      |      |      |      |            |       |       |
| ov/ |    |      |      |      |      |            |       |       |
| ohx |    |      |      |      |      |            |       |       |
| /re |    |      |      |      |      |            |       |       |
| sea |    |      |      |      |      |            |       |       |
| rch |    |      |      |      |      |            |       |       |
| /el |    |      |      |      |      |            |       |       |
| _ni |    |      |      |      |      |            |       |       |
| no/ |    |      |      |      |      |            |       |       |
| app |    |      |      |      |      |            |       |       |
| end |    |      |      |      |      |            |       |       |
| ix1 |    |      |      |      |      |            |       |       |
| .ht |    |      |      |      |      |            |       |       |
| m#t |    |      |      |      |      |            |       |       |
| abl |    |      |      |      |      |            |       |       |
| e8) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 6  | 0.8  | -6.6 | Near | St   | 1.06       | Very  | S     |
| N   |    |      |      | no   | able |            | wet   | table |
| iño |    |      |      | rmal |      |            |       |       |
| 19  |    |      |      |      |      |            |       |       |
| 76- |    |      |      |      |      |            |       |       |
| 197 |    |      |      |      |      |            |       |       |
| 7]( |    |      |      |      |      |            |       |       |
| htt |    |      |      |      |      |            |       |       |
| p:/ |    |      |      |      |      |            |       |       |
| /ww |    |      |      |      |      |            |       |       |
| w.s |    |      |      |      |      |            |       |       |
| rh. |    |      |      |      |      |            |       |       |
| noa |    |      |      |      |      |            |       |       |
| a.g |    |      |      |      |      |            |       |       |
| ov/ |    |      |      |      |      |            |       |       |
| ohx |    |      |      |      |      |            |       |       |
| /re |    |      |      |      |      |            |       |       |
| sea |    |      |      |      |      |            |       |       |
| rch |    |      |      |      |      |            |       |       |
| /el |    |      |      |      |      |            |       |       |
| _ni |    |      |      |      |      |            |       |       |
| no/ |    |      |      |      |      |            |       |       |
| app |    |      |      |      |      |            |       |       |
| end |    |      |      |      |      |            |       |       |
| ix1 |    |      |      |      |      |            |       |       |
| .ht |    |      |      |      |      |            |       |       |
| m#t |    |      |      |      |      |            |       |       |
| abl |    |      |      |      |      |            |       |       |
| e9) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 5  | 0.8  | -2.6 | Near | Coo  | 1.39       | Very  | S     |
| N   |    |      |      | no   | ling |            | wet   | table |
| iño |    |      |      | rmal |      |            |       |       |
| 197 |    |      |      |      |      |            |       |       |
| 7-1 |    |      |      |      |      |            |       |       |
| 978 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 10) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 14 | 2.3  | 2.7  | Near | St   | 0.92       | Near  | Decre |
| N   |    |      |      | no   | able |            | n     | asing |
| iño |    |      |      | rmal |      |            | ormal |       |
| 198 |    |      |      |      |      |            |       |       |
| 2-1 |    |      |      |      |      |            |       |       |
| 983 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 11) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 19 | 1.3  | 0.6  | Near | St   | 0.79       | Very  | Ra    |
| N   |    |      |      | no   | able |            | dry   | pidly |
| iño |    |      |      | rmal |      |            |       | decre |
| 198 |    |      |      |      |      |            |       | asing |
| 6-1 |    |      |      |      |      |            |       |       |
| 988 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 12) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
|     |    | 1.6  | 0.7  | Near | St   | 0.54       | Very  | Ra    |
|     |    |      |      | no   | able |            | dry   | pidly |
|     |    |      |      | rmal |      |            |       | decre |
|     |    |      |      |      |      |            |       | asing |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 14 | 1.8  | 2.3  | Near | St   | 0.93       | Near  | Ra    |
| N   |    |      |      | no   | able |            | n     | pidly |
| iño |    |      |      | rmal |      |            | ormal | incre |
| 199 |    |      |      |      |      |            |       | asing |
| 1-1 |    |      |      |      |      |            |       |       |
| 992 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 13) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 5  | 0.8  | -0.  | Near | St   | 0          | Near  | Incre |
| N   |    |      | 9^\* | no   | able | .99^\*(4)^ | n     | asing |
| iño |    |      | (4)^ | rmal |      |            | ormal |       |
| 1   |    |      |      |      |      |            |       |       |
| 993 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 14) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 12 | 1.3  | 2.4  | Warm | St   | 0.95       | Near  | Incre |
| N   |    |      |      |      | able |            | n     | asing |
| iño |    |      |      |      |      |            | ormal |       |
| 199 |    |      |      |      |      |            |       |       |
| 4-1 |    |      |      |      |      |            |       |       |
| 995 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 15) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 12 | 2.5  | 0.2  | Near | St   | 1.12       | Wet   | S     |
| N   |    |      |      | no   | able |            |       | table |
| iño |    |      |      | rmal |      |            |       |       |
| 199 |    |      |      |      |      |            |       |       |
| 7-1 |    |      |      |      |      |            |       |       |
| 998 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 16) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+
| [El | 11 | 1.5  | -0.4 | Warm | St   | 1.21       | Near  | Incre |
| N   |    |      |      |      | able |            | n     | asing |
| iño |    |      |      |      |      |            | ormal |       |
| 200 |    |      |      |      |      |            |       |       |
| 2-2 |    |      |      |      |      |            |       |       |
| 003 |    |      |      |      |      |            |       |       |
| ](h |    |      |      |      |      |            |       |       |
| ttp |    |      |      |      |      |            |       |       |
| :// |    |      |      |      |      |            |       |       |
| www |    |      |      |      |      |            |       |       |
| .sr |    |      |      |      |      |            |       |       |
| h.n |    |      |      |      |      |            |       |       |
| oaa |    |      |      |      |      |            |       |       |
| .go |    |      |      |      |      |            |       |       |
| v/o |    |      |      |      |      |            |       |       |
| hx/ |    |      |      |      |      |            |       |       |
| res |    |      |      |      |      |            |       |       |
| ear |    |      |      |      |      |            |       |       |
| ch/ |    |      |      |      |      |            |       |       |
| el_ |    |      |      |      |      |            |       |       |
| nin |    |      |      |      |      |            |       |       |
| o/a |    |      |      |      |      |            |       |       |
| ppe |    |      |      |      |      |            |       |       |
| ndi |    |      |      |      |      |            |       |       |
| x1. |    |      |      |      |      |            |       |       |
| htm |    |      |      |      |      |            |       |       |
| #ta |    |      |      |      |      |            |       |       |
| ble |    |      |      |      |      |            |       |       |
| 17) |    |      |      |      |      |            |       |       |
+-----+----+------+------+------+------+------------+-------+-------+

[Note:]{.underline} In Tables 3a and 3b, an asterisk (\*) indicates an
ENSO event where the \"pre-SST Max periods\" were not sufficient to
calculate an average for a full PL~avg~. The corresponding number in
parentheses indicates the number of periods for each less-than-optimal
case that was used for the calculation.

+-----+----+------+------+------+-------+------------+------+-------+
| *   |    |      |      |      |       |            |      |       |
| *Ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 3b. |    |      |      |      |       |            |      |       |
| S   |    |      |      |      |       |            |      |       |
| umm |    |      |      |      |       |            |      |       |
| ary |    |      |      |      |       |            |      |       |
| of  |    |      |      |      |       |            |      |       |
| La  |    |      |      |      |       |            |      |       |
| N   |    |      |      |      |       |            |      |       |
| iña |    |      |      |      |       |            |      |       |
| O   |    |      |      |      |       |            |      |       |
| ccu |    |      |      |      |       |            |      |       |
| rre |    |      |      |      |       |            |      |       |
| nce |    |      |      |      |       |            |      |       |
| s** |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| **E | *  | **   | *    |      |       | **Pre      |      |       |
| ven | *P | Maxi | *Tem |      |       | cipitation |      |       |
| t** | er | mum\ | pera |      |       | Charact    |      |       |
|     | io | SST\ | ture |      |       | eristics** |      |       |
|     | ds | A    | C    |      |       |            |      |       |
|     | ** | noma | hara |      |       |            |      |       |
|     |    | ly** | cter |      |       |            |      |       |
|     |    |      | isti |      |       |            |      |       |
|     |    |      | cs** |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
|     |    |      | **   | *    | *     | **Ratio of | *    | *     |
|     |    |      | Aver | *Pre | *∆T** | observed   | *Pre | *∆P** |
|     |    |      | age\ | vail |       | pre        | vail |       |
|     |    |      | o    | ing\ |       | cipitation | ing\ |       |
|     |    |      | bser | sho  |       | to         | sho  |       |
|     |    |      | ved\ | rt-\ |       | normal**   | rt-\ |       |
|     |    |      | de   | t    |       |            | t    |       |
|     |    |      | part | erm\ |       |            | erm\ |       |
|     |    |      | ure\ | c    |       |            | c    |       |
|     |    |      | f    | lima |       |            | lima |       |
|     |    |      | rom\ | te** |       |            | te** |       |
|     |    |      | norm |      |       |            |      |       |
|     |    |      | al** |      |       |            |      |       |
|     |    |      |      |      |       |            |      |       |
|     |    |      | *    |      |       |            |      |       |
|     |    |      | *for |      |       |            |      |       |
|     |    |      | P    |      |       |            |      |       |
|     |    |      | L~av |      |       |            |      |       |
|     |    |      | g~** |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 15 | -1.8 | 2.   | Near | S     | 1          | Near | Incre |
| N   |    |      | 4^\* | no   | table | .63^\*(3)^ | no   | asing |
| iña |    |      | (3)^ | rmal |       |            | rmal |       |
| 195 |    |      |      |      |       |            |      |       |
| 0-1 |    |      |      |      |       |            |      |       |
| 951 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 18) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 34 | -2.1 | -1.1 | Near | Wa    | 1.04       | Near | Decre |
| N   |    |      |      | no   | rming |            | no   | asing |
| iña |    |      |      | rmal |       |            | rmal |       |
| 195 |    |      |      |      |       |            |      |       |
| 4-1 |    |      |      |      |       |            |      |       |
| 957 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 19) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 8  | -0.6 | -0.  | Very | Co    | 0          | Near | S     |
| N   |    |      | 6^\* | cool | oling | .77^\*(3)^ | no   | table |
| iña |    |      | (3)^ |      |       |            | rmal |       |
| 196 |    |      |      |      |       |            |      |       |
| 1-1 |    |      |      |      |       |            |      |       |
| 962 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 20) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 11 | -1.1 | -0.9 | Very | S     | 1.01       | Near | S     |
| N   |    |      |      | cool | table |            | no   | table |
| iña |    |      |      |      |       |            | rmal |       |
| 196 |    |      |      |      |       |            |      |       |
| 4-1 |    |      |      |      |       |            |      |       |
| 965 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 21) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 7  | -0.9 | -3.7 | Very | S     | 0.82       | Near | S     |
| N   |    |      |      | cool | table |            | no   | table |
| iña |    |      |      |      |       |            | rmal |       |
| 196 |    |      |      |      |       |            |      |       |
| 7-1 |    |      |      |      |       |            |      |       |
| 968 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 22) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 19 | -1.4 | -1.3 | Cool | Wa    | 0.78       | Near | Incre |
| N   |    |      |      |      | rming |            | no   | asing |
| iña |    |      |      |      |       |            | rmal |       |
| 197 |    |      |      |      |       |            |      |       |
| 0-1 |    |      |      |      |       |            |      |       |
| 972 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 23) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 15 | -2.0 | 4.2  | Near | S     | 1.38       | Near | Ra    |
| N   |    |      |      | no   | ignif |            | no   | pidly |
| iña |    |      |      | rmal | icant |            | rmal | incre |
| 197 |    |      |      |      | wa    |            |      | asing |
| 3-1 |    |      |      |      | rming |            |      |       |
| 974 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 24) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 21 | -1.8 | 2.5  | Near | S     | 1.08       | Very | Incre |
| N   |    |      |      | no   | table |            | wet  | asing |
| iña |    |      |      | rmal |       |            |      |       |
| 197 |    |      |      |      |       |            |      |       |
| 4-1 |    |      |      |      |       |            |      |       |
| 976 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 25) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 5  | -0.9 | -0.7 | Near | S     | 1.07       | Near | S     |
| N   |    |      |      | no   | table |            | no   | table |
| iña |    |      |      | rmal |       |            | rmal |       |
| 198 |    |      |      |      |       |            |      |       |
| 3-1 |    |      |      |      |       |            |      |       |
| 984 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 26) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 9  | -1.1 | -0.2 | Near | Wa    | 0.98       | Near | Decre |
| N   |    |      |      | no   | rming |            | no   | asing |
| iña |    |      |      | rmal |       |            | rmal |       |
| 198 |    |      |      |      |       |            |      |       |
| 4-1 |    |      |      |      |       |            |      |       |
| 985 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 27) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 13 | -1.9 | 0.9  | Near | Wa    | 1.02       | Very | Decre |
| N   |    |      |      | no   | rming |            | dry  | asing |
| iña |    |      |      | rmal |       |            |      |       |
| 198 |    |      |      |      |       |            |      |       |
| 8-1 |    |      |      |      |       |            |      |       |
| 989 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 28) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 7  | -0.8 | -1.8 | Near | Co    | 1.08       | Near | Incre |
| N   |    |      |      | no   | oling |            | no   | asing |
| iña |    |      |      | rmal |       |            | rmal |       |
| 199 |    |      |      |      |       |            |      |       |
| 5-1 |    |      |      |      |       |            |      |       |
| 996 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 29) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 24 | -1.6 | 2.9  | Near | Wa    | 1.14       | Near | S     |
| N   |    |      |      | no   | rming |            | no   | table |
| iña |    |      |      | rmal |       |            | rmal |       |
| 199 |    |      |      |      |       |            |      |       |
| 8-2 |    |      |      |      |       |            |      |       |
| 000 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
| .go |    |      |      |      |       |            |      |       |
| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 30) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+
|     |    | -1.6 | 3.0  | Near | Wa    | 0.75       | Near | S     |
|     |    |      |      | no   | rming |            | no   | table |
|     |    |      |      | rmal |       |            | rmal |       |
+-----+----+------+------+------+-------+------------+------+-------+
| [La | 5  | -0.7 | -2.  | Near | Wa    | 1          | Near | Incre |
| N   |    |      | 2^\* | no   | rming | .02^\*(4)^ | no   | asing |
| iña |    |      | (4)^ | rmal |       |            | rmal |       |
| 200 |    |      |      |      |       |            |      |       |
| 0-2 |    |      |      |      |       |            |      |       |
| 001 |    |      |      |      |       |            |      |       |
| ](h |    |      |      |      |       |            |      |       |
| ttp |    |      |      |      |       |            |      |       |
| :// |    |      |      |      |       |            |      |       |
| www |    |      |      |      |       |            |      |       |
| .sr |    |      |      |      |       |            |      |       |
| h.n |    |      |      |      |       |            |      |       |
| oaa |    |      |      |      |       |            |      |       |
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| v/o |    |      |      |      |       |            |      |       |
| hx/ |    |      |      |      |       |            |      |       |
| res |    |      |      |      |       |            |      |       |
| ear |    |      |      |      |       |            |      |       |
| ch/ |    |      |      |      |       |            |      |       |
| el_ |    |      |      |      |       |            |      |       |
| nin |    |      |      |      |       |            |      |       |
| o/a |    |      |      |      |       |            |      |       |
| ppe |    |      |      |      |       |            |      |       |
| ndi |    |      |      |      |       |            |      |       |
| x2. |    |      |      |      |       |            |      |       |
| htm |    |      |      |      |       |            |      |       |
| #ta |    |      |      |      |       |            |      |       |
| ble |    |      |      |      |       |            |      |       |
| 31) |    |      |      |      |       |            |      |       |
+-----+----+------+------+------+-------+------------+------+-------+

**6. Conclusions**

The objectives of this study have been two-fold. First, to develop a
method whereby the prevailing short-term climate and short-term climate
trend for Nashville, Tennessee, could be defined for any given year. The
derived terms \-- such as, \"cool,\" \"cooling,\" \"very warm\" and
\"warming\" \-- have been referred to as short-term \"climate signals.\"
Generally speaking, each year in the climate record could be represented
by its own unique pair of climate signals. However, the focus of this
study was narrow, involving only the years in which an El Niño or La
Niña occurred. The average observed weather in Nashville during each
ENSO event was then compared to the two derived climate signals for that
year. If the observed weather showed similar characteristics to either
of the two signals, the observed weather was designated as
\"non-anomalous.\" However, if the observed weather differed from *both*
short-term climate signals, the observed weather was labeled
\"anomalous.\"

In this study, the short-term climate was defined using two variables
\-- one to define the \"*prevailing* short-term climate\" and the other
to define the general *trend* in the short-term climate. The specific
temperature values used to define these two variables can be found in
[Appendix 3](http://www.srh.noaa.gov/ohx/research/el_nino/appendix3.htm)
under \"TEMPERATURE CHARACTERISTICS.\" The specific precipitation values
used to define these two variables can also be found in [Appendix
3](http://www.srh.noaa.gov/ohx/research/el_nino/appendix3.htm) under
\"PRECIPITATION CHARACTERISTICS.\"

*a. El Niño*

Table 3a summarizes the data for Nashville climate signals associated
with each El Niño occurrence between 1957 and 2003. It shows three times
when the temperature departure was \"warm\" or \"very warm,\" seven
times when the temperature departure was \"cool\" or \"very cool,\" and
six times when the observed temperature was near normal. Additionally,
there were nine significant departures (\>1.7^o^) and seven
insignificant departures ([\<]{.underline}1.7^o^).

The data in Table 3a show that El Niño occurrences were coincident with
average observed temperature departures from normal that were \"very
cool\" (i.e., observed temperatures greater than 1.7^o^ cooler than
normal) six out of sixteen times. Indeed, almost every observed average
for El Niño that fell below the "near normal" threshold (of 0.8^o^)
ended up "very cool," with only one event classified as merely "cool."
Thus, the record shows that whenever El Niños were observed to produce
relatively cool weather at Nashville, the cooling was *almost always*
significant.

Using our \"climate filter,\" we find that only one of the "very cool"
cases (1976-1977) was associated with an anomalous observed temperature
signal, when compared to the two short-term climate signals. In other
words, at least one of the short-term climate signals was similar to the
observed temperature signal in five of the six cases, which implies
there may have been other short-term climate fluctuations, unrelated to
El Niño, that were also affecting the weather at Nashville during that
time and, perhaps, amplifying the "cool" or "very cool" weather
experienced during El Niño.

Table 3a also shows that El Niño occurrences were coincident with
average observed temperature departures from normal that were \"very
warm\" (i.e., observed temperatures greater than 1.7^o^ warmer than
normal) three times. In two of these cases, the observed temperature
signal was anomalous to the two short-term climate signals (i.e., both
short-term climate signals were anomalous to the observed temperature
signal in two of the three cases).

**Finding #1:** In the absence of using a short-term \"climate filter,\"
it cannot be demonstrated that El Niño events between 1950 and 2003 (for
PL~avg~) were associated with either colder-than-normal or
warmer-than-normal conditions at Nashville, or with the significance of
the departure from normal. However, after applying a short-term
\"climate filter,\" there is strong evidence that El Niño events
accompanied by cooler-than-normal temperatures were almost always
associated with non-anomalous thermal conditions, where Nashville\'s
weather conditions could not be easily distinguished from the short-term
climate signals. Conversely, El Niño events accompanied by "very warm"
temperatures, in one small subset of three events, were associated with
anomalous thermal conditions 67% of the time.

When El Niño is accompanied by large, negative temperature departures
from normal at Nashville, the negative sign of the departure is usually
correlated with certain short-term climate signal combinations. For
instance, in the two cases where the prevailing short-term temperature
signal was near normal and the temperature trend signal exhibited
\"cooling,\" the observed average temperature during El Niño was \"very
cool.\" In three out of four cases when the prevailing short-term
temperature signal was \"cool\" and the temperature trend signal was
\"stable,\" the observed average temperature during El Niño was \"very
cool.\" Four out of these six cases occurred during the climatologically
cool period of the late 1950\'s through the 1960\'s. A fifth case
occurred during a short-term cooling between 1975 and 1980 (Figure 4b).

The same type of strong positive correlation just described (between the
short-term temperature signals and observed average temperatures that
were \"very cool\") could not be found when observed average
temperatures during El Niño were \"very warm.\" In fact, such El Niño
events usually indicated anomalous conditions, deviating from the
short-term climate that was "near normal" and "stable."

Finally, during five of the seven times when the two temperature signals
were \"near normal\" and \"stable,\" the El Niño weather at Nashville
was "warm" or "very warm." Only twice was the weather "cool" or "very
cool." Stated another way, the data suggest that when both climate
signals are \"near normal\" and \"stable,\" observed weather is unlikely
to be \"cool\" or \"very cool.\" Another interesting feature in the data
is that since 1980, there have been seven El Niños, with only one
associated with "cool" observed conditions. Indeed, all three El Niños
with "very warm" weather occurred after 1980.

Based on these findings, we conclude there are strong indications that
the observed average temperatures at Nashville during El Niño events are
closely tied to the short-term temperature signals. The absence of a
\"warm\" or \"warming\" signal and the presence of either a \"cool\"
prevailing short-term climate or a short-term trend that exhibits
\"cooling\" suggest the likelihood of \"very cool\" observed thermal
conditions at Nashville. History has verified this scenario five out of
six times. On the other hand, when short-term temperature signals are
either "warm" or "warming,\" the average observed temperatures at
Nashville during El Niño are likely to range from "near normal" to "very
warm.\" History verified this scenario two out of three times. Finally,
when the short-term temperature signals are both \"near normal\" and
\"stable\" it is likely that the observed climate signal at Nashville
will range from "near normal" to "very warm." History has verified this
scenario five out of seven times.

We are also reminded of an intrinsic problem involved with any
investigation that attempts to uncover correlations between observed
temperature conditions at a particular station or group of stations and
El Niño events: certain correlations may be missed if it is assumed they
will exhibit a simple one-to-one relationship. Indeed, as shown with
this investigation of the temperature signals at Nashville during El
Niño events, it is clear that the use of a \"climate filter\" \-- to
place particular temperature observations in context with ongoing
changes in the short-term climate (that have longer periodicity than
those associated with El Niño) \-- may actually yield important
correlations; correlations that would be masked without the use of a
\"climate filter.\"

With respect to precipitation, Table 3a shows four El Niño events where
the ratio of observed precipitation to normal was \>1.07 (\"wet\" or
\"very wet\"), six times when the ratio was \<0.93 (\"dry\" or \"very
dry\"), and six times when the ratio was normal
(0.93[\<]{.underline}ratio[\<]{.underline}1.07).

El Niño occurrences were coincident with average observed precipitation
departures from normal that were \"very wet\" (i.e., observed
precipitation more than 115% of normal) three times. In none of these
cases was the observed precipitation signal anomalous to the two
short-term climate signals (i.e., at least one of the short-term climate
signals was similar to the observed precipitation signal in each of the
three cases).

The data in Table 3a show that El Niño occurrences were coincident with
average observed precipitation departures from normal that were \"very
dry\" (i.e., observed precipitation less than 85% of normal) four out of
sixteen times. Using our \"climate filter,\" we find that only one of
these cases (El Niño 1963-1964) represents a precipitation anomaly that
was different from both short-term climate signals. In other words, at
least one of the short-term climate signals was similar to the observed
precipitation signal in three of the four cases, which implies there may
have been other short-term climate fluctuations, unrelated to El Niño,
that were also affecting the weather at Nashville during those times
and, perhaps, amplifying the dry conditions experienced during El Niño.

As discussed earlier, and revealed in Tables 2a and 2b, there is usually
a noticeable trend in precipitation at Nashville during El Niño events
highlighted by above-normal precipitation during the late summer and/or
early fall (in the September-October period). Our research further shows
this rainfall maximum is usually followed by a drying trend, which tends
to reach a maximum during the period from late fall through early
spring. Historically, this holds true for ENSO events that reach maximum
anomaly between the periods OND and DJF (i.e., exhibit late-year
maxima). As shown in Table 2a, there was only one case where the maximum
anomaly occurred at some other time of the year. That was during the
second maximum anomaly that occurred during the long ENSO of 1986 to
1988, when the maximum anomaly occurred during the summertime JAS
period.

When using the expanded subset of 14 El Niños (Table 2b), where the
pre-SST Max ENSO record was extended to include the \"ENSO Max -- 1\"
period, we find that either September or October (or both) had
above-normal precipitation 79% of the time, with at least one of the
months often showing rainfall that was equal to or greater than 140% of
normal.

Thus, there seems to be a wetter-than-normal precipitation signal for
the September-October period during the late summer and early fall, just
before a drying trend sets in for the ENSO Max period during the late
fall, winter, and early spring. However, since the drying trend is
relative to the magnitude of the Pre-ENSO Max wet period, the
three-month composite average that coincides with the SST maximum may
still be associated with normal or, in some cases, even above-normal
precipitation; which occurred in 7 out of 13 cases, or approximately
half the time. (See "Precipitation Data" in Tables 5-19.) Yet, it is
important to note that in all 6 of those cases, the drying trend
continued during the Post-ENSO Max period, with subsequent running means
often dropping below normal for 2 to 3 successive periods immediately
preceding the SST maximum. Thus, a period of below normal precipitation
is most likely during the period extending from the ENSO maximum to 3
periods afterwards, encompassing a stretch of time between late fall and
early spring.

In the expanded subset of 16 El Niños (Table 2a), two cases showed up
where a Pre-ENSO Max period (which included September and/or October),
was characterized by a 3-month precipitation average that was either
near normal or below normal (in 1965 and 1982). These represented
exceptions to the general rule, and Table 3a shows they occurred during
times when the prevailing short-term climate at Nashville was \"near
normal\" and the prevailing short-term precipitation trend was
\"decreasing.\" In fact, there was only one case (out of four) when a
dry climate signal(s) was in place and, yet, wet conditions were
observed during the pre-ENSO Max period (for the three-month composite
which included September and/or October). That was in 1986, during the
first maximum anomaly of the long El Niño of 1986 to 1988.

Thus, it appears that as long as the weather at Nashville is not under
the influence of another climatic phenomenon characterized by relatively
dry conditions, the El Niño SST maximum will be preceded by relatively
wet conditions in the late summer and early fall (in either September or
October, or both). Additional support was given for this conclusion
earlier, when it was stated that there was only one case in the record
where \"very dry\" weather during an El Niño (for the PL~avg~ period)
exhibited an anomaly when compared to the short-term climate signals.
That occurred in 1963. The three other times when very dry conditions
were observed, the observed El Niño conditions were in sync with the
prevailing drought (in 1965, 1986, and 1987). Nevertheless, despite the
relative dryness of the main part of El Niño 1986, there was still a wet
pre-ENSO Max period (which included the month of October). Precipitation
during the pre-ENSO Max period (OND 1986) ended up 13% above normal.

**Finding #2:** In the absence of using a short-term \"climate filter,\"
it cannot be demonstrated that El Niño events between 1950 and 2003 (for
the PL~avg~ period) were associated with either drier-than-normal or
wetter-than-normal conditions at Nashville, or with the significance of
the departure from normal. In addition, even after applying a short-term
\"climate filter\" there is very little evidence that El Niño events are
associated with anomalous precipitation conditions, where Nashville\'s
weather conditions can be easily distinguished from either one or both
of the two short-term precipitation signals.

However, it can be demonstrated that when large negative departures from
normal are coincident with El Niño (i.e., Nashville\'s weather is \"very
dry\"), the sign of the departure may very well be correlated with
certain short-term precipitation signals. For instance, in three out of
four cases when the observed precipitation signal was \"very dry,\" at
least one of the short-term climate signals was in sync with the
observed precipitation signal (i.e., the prevailing short-term climate
was \"very dry\" and/or the short-term trend was \"decreasing\" or
\"rapidly decreasing\"). The short-term precipitation *trend* signal
appears more closely associated with dry El Niño conditions at Nashville
than the prevailing short-term precipitation signal. For instance, in
four of the four documented cases when El Niño events occurred
simultaneously with a short-term precipitation trend signal
characterized as \"decreasing\" or \"rapidly decreasing,\" the observed
precipitation was \"dry\" (1 time) or \"very dry\" (3 times). The
departures ranged from 8% below normal to 46% below normal. The only
prevailing short-term precipitation signal that occurred exclusively
with drier-than-normal El Niño weather at Nashville was the one
characterized as \"very dry\" (observed on two occasions during El Niño
1986-1988).

The same type of correlation just described (between the short-term
precipitation trend signal and average observed precipitation during El
Niño that was \"dry\" or \"very dry\") could not be found for average
observed precipitation during El Niño that was "wet" or \"very wet.\"
However, a similar-type correlation did show up between a certain
*prevailing* short-term precipitation signal and observed "wet" or "very
wet" conditions during El Niño. Each of the three times that a "wet" or
"very wet" signal showed up, the observed precipitation was above
normal, ranging from "near normal" to "very wet."

Based on these findings, we conclude that there are indications that
when the \"short-term climate trend\" signal is \"decreasing\" or
\"rapidly decreasing,\" the observed precipitation signal at Nashville
during El Niño events will likely be \"dry/very dry.\" History has
verified this scenario four out of four times. This does not mean,
however, that there will be no "pre-SST Max" rainfall maximum (similar
to the one that occurred in OND, 1986).

In addition, whenever the prevailing short-term precipitation was "very
dry," the observed precipitation during El Niño was "very dry." Whenever
the prevailing short-term precipitation was "wet" or "very wet," the
observed precipitation was above normal (ranging from "near normal" to
"very wet"). Thus, 44% of El Niños at Nashville were associated with
precipitation that was in sync with certain specific short-term climate
signals. However, in the absence of those signals, the associations
between observed precipitation and short-term climate were ambiguous.

One prominent feature that shows up in the El Niño precipitation record
is a general drying trend that occurs between a relative maximum in
precipitation, usually observed in the September-October period, and a
relative minimum, usually observed between late fall and early spring.
At some point during the SST maximum, or within three periods after the
maximum, precipitation amounts can generally be expected to fall below
normal.

**Finding #3:** To summarize Table 3a, we conclude that El Niño events
during the 1950-2003 period did not have a clearly defined anomalous
impact on the average observed temperature at Nashville, Tennessee (for
the PL~avg~ period); or, at least, there is no anomalous effect that can
be distinguished from normal short-term climate variability. However,
there is evidence that if an El Niño develops when certain short-term
temperature signals are already in place, the observed temperature
signal at Nashville will reflect those same signals \-- often in an
amplified fashion.

There is only limited correlation between the short-term precipitation
signals and the average observed precipitation at Nashville during El
Niño. In this limited data set there appears to be a relationship
between a short-term precipitation *trend* signal that is \"decreasing\"
or \"rapidly decreasing\" and average observed precipitation that is
\"dry\" or \"very dry.\" It is interesting that there also appears to be
a cross-correlation with these particular drought trends in the
short-term climate (\"decreasing\" or \"rapidly decreasing\") and
certain average observed temperature patterns at Nashville. These
drought trends were associated with average observed temperatures during
El Niño that were \"near normal\" three times, and "much
warmer-than-normal\" once. Thus, each El Niño that occurred when ∆P
indicated short-term drying was associated with observed temperatures
ranging from near normal to very warm -- never with "cool" or "very
cool" conditions. Otherwise, no clear cross-correlation between the El
Niño temperature and precipitation data sets was found. For instance,
the data do not reveal the existence of certain climate combinations,
such as \"cool\" and \"dry\" or \"warm\" and \"dry,\" that might be
expected to show up in Nashville\'s weather during El Niño events. In
addition to these "dry" signals, a certain "wet" signal also showed up
that was correlated with above-normal observed precipitation. This type
of El Niño weather occurred each of the three times that the prevailing
climate signal was "wet" or "very wet."

[Note:]{.underline} By the time this study was completed, in 2008, two
additional El Niños had occurred outside the time range of data depicted
in Appendix 1. The first occurred between "JJA, 2004" and "JFM, 2005."
The maximum anomaly occurred in "ASO, 2004." Since the "pre-ENSO Max"
period did not include the months of September and October, the theory
regarding a wet September and/or wet October, followed by a drying
trend, could not be tested. However, a second El Niño occurred between
"JAS, 2006" and "DJF, 2007" and exhibited a maximum anomaly in "OND,
2006." Since September and October both fell during the "pre-ENSO Max"
period, we were able to test the theory. The results showed a positive
verification, with a maximum rainfall during the "ASO, 2006" period
(3.69 inches above normal), and a consistent drying trend thereafter
(through "DJF, 2007").

*b. La Niña*

The investigation of La Niña parallels the one already discussed for El
Niño. The same objectives exist and the same procedures were used,
including ones intended to determine if the type of weather that
occurred during La Niña events was anomalous to the prevailing
short-term climate conditions.

Just as in the previous section on El Niño, the prevailing climate
conditions were defined using two variables \-- one to define the
\"*prevailing* short-term climate\" and the other to define the general
\"*trend* in the short-term climate\". The specific temperature values
used to define these two variables can be found in Appendix 3 under
\"TEMPERATURE CHARACTERISTICS.\"

Table 3b summarizes the data for Nashville climate signals associated
with each La Niña occurrence between 1950 and 2001. It shows six times
when the observed temperature departure from normal was at least 0.7^o^
(\"warm\" or \"very warm\"), seven times when the temperature departure
was at least -0.7^o^ (\"cool\" or \"very cool\"), and two times when the
observed temperature was \"normal\" or \"near normal\"
([\>]{.underline}-0.6^o^, but [\<]{.underline}0.6^o^). In addition,
there were nine La Niñas where the observed temperature exhibited
significant departures from normal (\>\|1.2^o^\|), but only six
instances where departures from normal were insignificant
([\<]{.underline}\|1.2^o^\|). Thus, significant departure from normal
occurred with a 50% greater frequency than insignificant departures.

The data in Table 3b show that La Niña occurrences were coincident with
average observed temperature departures from normal that were \"very
cool\" (i.e., observed temperatures more than 1.2^o^ below normal) four
out of 15 times. Using our \"climate filter,\" only one of these cases
was shown to be associated with an anomalous observed temperature
signal, when compared to the two short-term climate signals. This
occurred during the La Niña of 2000-2001. The very cool weather observed
during the La Niña of 2000-2001 occurred when the prevailing short-term
climate signal was \"near normal\" and the trend signal was \"warming.\"
In the remaining two cases, at least one of the short-term climate
signals was similar to the average observed temperatures during La Niña;
which implies there may have been other short-term climate fluctuations,
unrelated to La Niña, that were also affecting the weather at Nashville
during that time and, perhaps, amplifying the cool conditions
experienced during La Niña.

Table 3b also shows that La Niña occurrences were coincident with
average observed temperature departures that were \"very warm\" (i.e.,
observed temperatures more than 1.2^o^ above normal) five times. Two of
these cases were associated with an anomalous observed temperature
signal when compared to the two short-term climate signals (La Niñas of
1950-1951 and 1974-1976). Both of those La Niñas occurred when the
prevailing short-term climate signal was \"near normal\" and the trend
signal was \"stable.\" In the remaining three cases, at least one of the
short-term climate signals was similar to the average observed
temperature, which implies there may have been other short-term climate
fluctuations unrelated to La Niña that were also affecting the weather
at Nashville during those times and, perhaps, amplifying the warm
conditions experienced during La Niña.

**Finding #1:** In the absence of using a short-term \"climate filter,\"
it cannot be demonstrated that La Niña events are associated with either
colder-than-normal or warmer-than-normal conditions in Nashville. There
is, however, evidence to suggest that observed temperatures during
previous La Niñas tended to exhibit significant departures from normal
with greater frequency than insignificant departures.

After applying a short-term \"climate filter,\" there is only a
relatively small subset of La Niña events associated with anomalous
thermal conditions where Nashville\'s weather conditions can be easily
distinguished from either one or both of the two short-term climate
signals. However, just as demonstrated with El Niño, it can be shown
that certain types of observed weather are typically associated with
particular short-term climate signal combinations. For instance, there
were nine La Niñas when the average observed departure from normal was
negative (ranging from -0.2^o^ to -3.7^o^). In five of those cases (56%
of the total), at least one of the climate signals indicated \"cool,\"
\"very cool,\" or \"cooling\" conditions. Perhaps more importantly,
*every* time one of the short-term climate signals was \"cool,\" \"very
cool,\" or \"cooling,\" the observed conditions were in sync (i.e., the
observed conditions were below normal). This correlation is very similar
to the one found for El Niños that occurred during the climatologically
cool period of the late 1950's and 1960\'s. Indeed, the three times when
La Niña occurred during a prevailing short-term climate that was "very
cool" were sandwiched in the 1960's, with observed conditions ranging
from "near normal" to "very cool."

In addition to the subset of data just mentioned, involving La Niñas
that occurred when the short-term climate signals were \"cool,\" \"very
cool,\" or \"cooling,\" there is a large subset of data where the
prevailing short-term climate was \"near normal\" and the short-term
trend was either \"stable\" or \"warming/significant warming.\" In fact,
these signal combinations comprised the remainder of the La Niña record
(ten cases), and are the most prevalent signal combinations associated
with La Niña at Nashville. There were seven times when the combination
was \"near normal\" and \"warming/significant warming\" and three times
when the combination was \"near normal\" and \"stable.\" In 60% of these
ten cases the observed departure from normal was positive and often (83%
of this subset) indicated \"very warm\" conditions. Only one positive
departure in this subset was less than 2.4^o^, or two standard
deviations. In fact, of the times when positive departures occurred with
these signal combinations, the average departure for all six cases was
an impressive 2.7^o^. In the four remaining cases that were cooler than
normal, the average negative departure was just 1.1^o^, with only a
single case when the average observed departure was \"very cool\" (La
Niña 2000-2001).

In summary, we find the following correlation statistics for La Niña:

1). In all five cases (100% of the time) when one of the climate signals
was \"cool,\" \"very cool,\" or \"cooling,\" the observed conditions
were in phase (i.e., the observed conditions were below normal).

2). In the remaining ten cases, the signal combination was either \"near
normal\" and \"warming/significant warming\" (7 times) or \"near
normal\" and \"stable\" (3 times). In 60% of these cases the observed
departure was positive, and often indicative of extreme warmth or \"very
warm\" conditions. In the remaining 40% of the cases, where negative
departures were observed, there was only a single case when the observed
chill was \"very cool.\" Most of the cool weather was only slight to
moderate.

We have already seen that when La Niña is accompanied by observed
weather that is warmer than normal, it is often \"very warm.\" Thus, it
would be useful if a unique climate signal could be found in the
temperature record that would help Nashville forecasters realize when a
\"very warm\" La Niña is likely unfolding or about to unfold. In a
similar way, we observed the \"wet-type\" September/October signal
preceding an El Niño drying trend.

Upon closer scrutiny of the record of three-month running means for each
La Niña, a unique climate signal can be isolated. If one looks at the
three three-month periods that occur shortly before the SST Max, there
is a strong tendency for two successive three-month running means to
indicate significant positive departures from normal (\>1.2^o^). This
long period of \"very warm\" weather typically occurs between late
summer (the \"JAS\" period) and early winter (the \"NDJ\" period). If
one is confident that the La Niña is approaching its maximum SST and two
successive three-month running means appear that indicate *significant
warmth*, there is a strong likelihood that a \"very warm\" La Niña is in
the early stages of unfolding. Such a signal occurred four times in the
La Niña record, with all four of them associated with an unusually long
period of \"very warm\" weather at Nashville, extending well past the
SST Max. When this criteria was met (i.e., this \"unique signal\" was
observed), there were three to six subsequent periods, after the SST
Max, where the three-month running means were \"very warm,\" generally
extending from late fall (the \"OND\" period) all the way through early
spring (the \"FMA\" period). Again, based on the La Niña record, this
signal was correlated with an unusually long period of \"very warm\"
conditions 100% of the time. Even though this signal did not give
advance indication of the onset of \"very warm\" conditions, it usually
showed up during the late summer and fall and indicated that an
unusually long period of \"very warm\" conditions was underway and would
likely last through the upcoming winter and early spring. Also, as
indicated in Section 5, there is some evidence to suggest that the
increasing warmth is also most likely if the SST anomaly is \>0.5^o^.

[Note:]{.underline} As this study was nearing completion, during the
late summer and early fall of 2007, a strong La Niña was unfolding. The
five, three-month periods between JAS and OND (2007) provided multiple
consecutive cases where the "very warm" temperature signal showed up.
Thus, based on the theory just presented, it was assumed that a "very
warm" La Niña was in the process of unfolding. If positive verification
of this theory was to occur, the periods "OND, 2007" through "FMA, 2008"
would necessarily have to reveal "very warm" conditions. In the final
analysis, four out of five of those periods were "very warm" and one was
"near normal." Although, the forecast wasn't perfect (i.e., five out of
five periods exhibiting "very warm" conditions), it was nearly perfect
(i.e., four out of five periods verified as "very warm"). Indeed, the
average departure for all five periods turned out to be +3.4^o^. Thus,
it appears that the original theory may be quite useful in determining
when an unfolding La Niña is likely to produce an extended period of
very warm conditions at Nashville, extending from late summer through
early spring.

  -------------------------------------------------------------------------------- ---------- -------------- ---------- ------------------- ----------------
  **Table 4. La Niña Events Exhibiting Significant Warmth**                                                                                 

  **Event**                                                                        **SST\     **Two warmest             **Successive        **Average warmth
                                                                                   Max\       consecutive               back-to-back        following the
                                                                                   period**   periods within            periods with \"very \"very warm\"
                                                                                              the SST Max -             warm\" weather**    signal**
                                                                                              3 window**                                    

  [La Niña                                                                         DJF\       Cannot be                 N/A                 N/A
  1950-1951](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table18)   1950       determined\*                                  

  [La Niña                                                                         OND\       2.6^o^ (JAS)   1.1^o^     Criteria not        Criteria not met
  1954-1957](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table19)   1955                      (ASO)      met\*\*             

  [La Niña                                                                         ASO\       Cannot be                 N/A                 N/A
  1961-1962](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table20)   1961       determined                                    

  [La Niña                                                                         SON\       -1.2^o^ (JJA)  -1.7^o^    Criteria not met    Criteria not met
  1964-1965](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table21)   1964                      (JAS)                          

  [La Niña                                                                         JFM\       -1.7^o^ (OND)  -3.0^o^    Criteria not met    Criteria not met
  1967-1968](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table22)   1968                      (NDJ)                          

  [La Niña                                                                         DJF\       1.3^o^ (SON)   0.7^o^     Criteria not met    Criteria not met
  1970-1972](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table23)   1971                      (OND)                          

  [La Niña                                                                         NDJ\       3.0^o^ (ASO)   5.3^o^     6 (OND -- MAM)      +3.3^o^
  1973-1974](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table24)   1973                      (SON)                          

  [La Niña                                                                         NDJ\       2.5^o^ (OND)   1.5^o^     3 (DJF -- FMA)      +4.5^o^
  1974-1976](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table25)   1975                      (NDJ)                          

  [La Niña                                                                         OND\       Cannot be                 N/A                 N/A
  1983-1984](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table26)   1983       determined                                    

  [La Niña                                                                         NDJ\       Cannot be                 N/A                 N/A
  1984-1985](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table27)   1984       determined                                    

  [La Niña                                                                         OND\       2.0^o^ (JAS)   -0.7^o^    Criteria not met    Criteria not met
  1988-1989](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table28)   1988                      (ASO)                          

  [La Niña                                                                         NDJ\       1.2^o^ (ASO)   -2.5^o^    Criteria not met    Criteria not met
  1995-1996](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table29)   1995                      (SON)                          

  [La Niña                                                                         DJF\       3.6^o^ (SON)   2.6^o^     3 (NDJ -- JFM)      +3.6^o^
  1998-2000](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table30)   1999                      (OND)                          

                                                                                   NDJ\       2.2^o^ (OND)   3.4^o^     3 (DJF -- FMA)      +3.4^o^
                                                                                   1999                      (NDJ)                          

  [La Niña                                                                         OND\       Cannot be                 N/A                 N/A
  2000-2001](http://www.srh.noaa.gov/ohx/research/el_nino/appendix2.htm#table31)   2000       determined                                    
  -------------------------------------------------------------------------------- ---------- -------------- ---------- ------------------- ----------------

\* If at least three three-month periods prior to the SST Max were not
part of the La Niña record, the criteria (i.e., the \"unique signal\")
could not be determined.

\*\* Provided the La Niña record included three three-month periods
prior to the SST Max, but two successive three-month running means of
sufficient warmth (i.e., departure from normal \>1.2^o^) did not occur,
the status of the unique signal was \"criteria not met.\"

With respect to precipitation, Table 3b shows three La Niña events where
the \"ratio of observed precipitation to normal\" indicated \"wet\" or
\"very wet\" conditions (≥1.09), four times when the ratio indicated
\"dry\" or \"very dry\" conditions (≤0.91), and eight times when the
ratio indicated normal or \"near normal\" conditions
(0.91\<ratio\<1.09).

The data in Table 3b show that La Niña occurrences were coincident with
average observed precipitation departures from normal that indicated
\"very dry\" conditions (i.e., observed precipitation less than 83% of
normal) four out of fifteen times. Using our \"climate filter,\" we find
all four cases associated with an anomalous observed precipitation
signal when compared to the two short-term precipitation signals.

Table 3b shows that La Niña occurrences were coincident with average
observed precipitation departures from normal that indicate \"very wet\"
conditions (i.e., observed precipitation more than 117% of normal) only
two times. Neither of these cases proved to be associated with an
anomalous observed precipitation during La Niña when compared to the two
short-term precipitation signals. The first case was associated with ∆P
= "increasing," the other with ∆P = "rapidly increasing." Of the six
times when ∆P showed similar signals in the La Niña record, five were
associated with above-normal precipitation, ranging from 2% to 63% above
normal.

**Finding #2:** In the absence of using a short-term \"climate filter,\"
it cannot be demonstrated that La Niña events between 1950 and 2001 (for
the PL~avg~ period) were associated with either drier-than-normal or
wetter-than-normal conditions at Nashville. There is, however, evidence
to suggest that observed temperatures during previous La Niñas tended to
exhibit significant departures from normal with greater frequency than
insignificant departures.

After applying a short-term \"climate filter,\" there is only a
relatively small subset of La Niña events associated with anomalous
precipitation conditions, where Nashville\'s observed weather conditions
can be easily distinguished from either one or both of the two
short-term precipitation signals.

Following is a summary of the general findings regarding the short-term
precipitation signals and observed precipitation at Nashville during
historical La Niña events, including: a) the likelihood of having
anomalous weather conditions, b) the predominant short-term
precipitation signals, and c) the cross-correlation between the
precipitation and temperature data sets.

a\) When the short-term precipitation signals were "very wet,"
"increasing," or "rapidly increasing," the observed weather during La
Niña was anomalous in only two of the six cases. This occurred during
the La Niñas of 1970-1972 and 1974-1976. During the first of these
events, the short-term precipitation signals were "near normal" and
"increasing," but the observed conditions were "very dry." During the
event of 1974-1976, the short-term signals were "very wet" and
"increasing," but the observed conditions were "near normal." In the
remaining four cases, the observed conditions were indistinguishable
from at least one of the short-term signals and were determined to be
non-anomalous.

The precipitation signal combination of "near normal" and "stable"
occurred on six occasions and was associated with anomalous observed
conditions during four of those events. Thus, anomalous conditions
occurred with only slightly greater frequency than non-anomalous
conditions when these two signals were in place.

The last remaining signal combinations for La Niña precipitation were
"near normal" and "decreasing," which occurred on two occasions, and
"very dry" and "decreasing," which occurred only once. The only
combination associated with anomalous observed conditions was "very dry"
and "decreasing," when the observed precipitation was "near normal."

Thus, when looking at the entire precipitation record for La Niña we
find that anomalous observed precipitation events occur with the same
relative frequency as non-anomalous events. Furthermore, the same
signals associated with anomalous events - if they occurred more than
once - were always associated with non-anomalous events as well. Thus,
the precipitation record for La Niña is highly ambiguous. However, as
mentioned earlier, there is some evidence to suggest that average
observed precipitation tends to be above-normal when ∆P is "increasing"
or "rapidly increasing."

b\) The most common prevailing short-term climate signal was "near
normal," which occurred on 13 out of 15 occasions. The short-term trend
signals, however, ran the gamut, ranging anywhere from "decreasing," to
"stable," to "rapidly increasing."

c\) Just like with El Niño, the La Niña climate record during the 1960's
showed some interesting temperature and precipitation correlations. The
three La Niñas that occurred during the 1960's all contained a
"cool-type" short-term temperature signal, and were always associated
with precipitation signals that were "near normal" and "stable." In
addition, the observed conditions were "very dry" (and anomalous) on two
of those three occasions. Thus, La Niñas during the 1960's tended to be
associated with cool and dry conditions at Nashville.

The only other distinct cross-correlation between temperature signals
and precipitation signals occurred with a short-term precipitation trend
that was "decreasing" and short-term temperature signals that were "near
normal" and "warming." In each of these three events, the observed
precipitation was near normal. The observed temperature, however, varied
anywhere from "cool" to "warm."

**Finding #3:** Based on the La Niña historical record, anomalous
observed precipitation conditions have occurred with virtually the same
frequency as non-anomalous conditions. Some of the most notable
anomalous events occurred during the climatologically peculiar period of
the 1960's, when "very dry" conditions were usually associated with
short-term precipitation signals that were "near normal" and "stable."
These conditions were also cross-correlated with the cooler-than-normal
temperatures of the 1960's.

When short-term temperature signals were not of the "cooling" variety,
anomalous observed precipitation patterns at Nashville (when compared to
the short-term precipitation signals) occurred with the same relative
frequency as non-anomalous patterns.

**Operational forecast applicability \-- A word of caution:** Can any of
these established scenarios be used to predict the general weather
conditions at Nashville during an upcoming El Niño or La Niña? As far as
trends in precipitation during El Niño events or extended very warm
spells during La Niña are concerned, the answer is likely \"yes.\"
However, based on the criteria used to define the short-term climate
signals in this study, the answer must otherwise be \"no.\" This is
largely due to the fact that someone making a forecast in the same year
that an El Niño event is occurring will not have access to all of the
five-year running mean annual data required to establish the short-term
climate signals. Remember, calculation of both the climate trend signal
and the prevailing climate signal involved the use of running means for
several \"post SST Maximum\" years. The data for these years, of course,
will be unknown at the time of the event. However, if a reasonable,
educated guess can be made regarding the applicable climate signals, the
following forecast flow charts could then be used to make a general
prediction:

**Flowchart for making seasonal or multi-month forecasts for Nashville
during El Niño events using prevailing short-term temperature and
temperature trends**

**Flowchart for making seasonal or multi-month forecasts for Nashville
during La Niña events using prevailing short-term precipitation and
precipitation trends**

*Acknowledgements*

*The authors thank the following individuals for their reviews and
assistance with this paper: Henry Steigerwaldt,
Science-and-Operations-Officer, and Larry Vannozzi,
Meteorologist-in-Charge, of the National Weather Service Office in
Nashville, Tennessee, Chris Darden, Science-and-Operations-Officer,
National Weather Service Office, Huntsville, Alabama, and Jon Zeitler,
Science-and-Operations-Officer, National Weather Service Office,
Austin/San Antonio, Texas.*

REFERENCES

Deedler, W.R., 1997: [El Niño\...will it live up to
expectations?](http://www.crh.noaa.gov/dtx/nino.htm) \[Available online
at <http://www.crh.noaa.gov/dtx/nino.htm>\]

Lussky, G., and T. Rieck, 1997: [The El
Niño](http://www.crh.noaa.gov/arx/enso.html). \[Available online at
<http://www.crh.noaa.gov/arx/enso.htm>\]

NASA, 2006: [What is El
Niño?](http://earthobservatory.nasa.gov/Library/ElNino). \[Available
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National Centers for Environmental Prediction (NCEP), Climate Prediction
Center, 2006: [Cold & Warm Episodes by
Season](http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml).
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National Centers for Environmental Prediction (NCEP), Climate Prediction
Center, 2007: [El Niño
Regions](http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/nino_regions.shtml).
\[Available online at
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National Weather Service (NWS), 2006: [El
Niño](http://ww2.wrh.noaa.gov/climate_info/ElNino_Page.htm) Page.
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Nunn, K.H. and A.T. DaGaetano, 2004: [The El Niño Southern Oscillation
and its role in cold-season tornado outbreak
climatology](http://ams.confex.com/ams/84Annual/techprogram/paper_71587.htm).
Amer. Met. Soc. *14th Conference on Applied Climatology*, JP5.2.
\[Available online at
<http://ams.confex.com/ams/84Annual/techprogram/paper_71587.htm>\]

Xue, Y., T.M. Smith, and R.W. Reynolds, 2003: Interdecadal Changes of
30-Yr SST Normals during 1871--2000, *J. Climate,* **16,** 1601-1612.
\[Available online at
http://www.cpc.ncep.noaa.gov/products/people/yxue/pub/13.html\]

**Appendix 1. Summary of El Niño events and related meteorological
data** []{#table3 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 5. El                                                                                                                        
  Niño                                                                                                                                 
  1957-1958**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1921-\     from\                    during\           (1921-\     of\        
                                         Period**        1950)**     Normal**                 Period**          1950)**     Total to\  
                                                                                                                            Normal**   

  1957          MAM          0.6         60.3            59.2        1.1            **TPM**   13.87             12.75       1.09       **TPM**

  1957          AMJ          0.7         70.0            68.3        1.7            1.0       18.08             10.66       1.70       1.45

  1957          MJJ          0.8         75.3            75.0        0.3            0.4       17.12             10.93       1.57       1.45

  1957          JJA          0.9         77.9            78.6        -0.7           -0.4      11.44             10.46       1.09       1.17

  1957          JAS          0.9         76.4            77.3        -0.9           -1.3      8.47              10.01       0.85       1.06

  1957          ASO          0.8         68.8            71.2        -2.4           -1.8      10.53             8.57        1.23       1.24

  1957          SON          0.9         59.2            61.4        -2.2           -1.8      14.29             8.67        1.65       1.50\*

  1957          OND          1.2         50.0            50.9        -0.9           -1.3\*    16.04             9.99        1.61       1.48

  1957          NDJ          1.5         42.8            43.5        -0.7           -1.9      14.75             12.40       1.19       1.19

  1958          DJF          1.6         37.2            41.2        -4.0           -4.0      10.05             13.15       0.76       0.84

  1958          JFM          1.5         36.9            44.1        -7.2           -5.8      8.13              14.37       0.57       0.74

  1958          FMA          1.1         44.7            50.8        -6.1           -5.2      11.88             13.13       0.90       0.83

  1958          MAM          0.7         56.8            59.2        -2.4           -3.2      12.99             12.75       1.02       1.03

  1958          AMJ          0.5         67.2            68.3        -1.1           -1.4      12.37             10.66       1.16       1.10

  1958          MJJ          0.5         74.4            75.0        -0.6                     12.17             10.93       1.11        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table4 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 6. El                                                                                                                        
  Niño                                                                                                                                 
  1963-1964**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1963          JJA          0.6         76.7            79.0        -2.3           **TPM**   16.05             9.83        1.63       **TPM**

  1963          JAS          0.8         74.8            77.5        -2.7           -1.8      16.39             9.45        1.73       1.58

  1963          ASO          0.8         70.8            71.1        -0.3           -0.8      11.06             8.05        1.37       1.26

  1963          SON          0.9         61.6            60.9        0.7            -0.6\*    5.86              8.47        0.69       0.84

  1963          OND          1.0         48.4            50.5        -2.1           -1.7      4.58              9.79        0.47       0.60

  1963          NDJ          1.0         39.5            43.2        -3.7           -3.8      8.28              12.96       0.64       0.58

  1964          DJF          0.8         35.5            41.1        -5.6                     9.11              14.19       0.64        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 7. El                                                                                                                        
  Niño                                                                                                                                 
  1965-1966**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1965          MJJ          0.6         75.1            75.4        -0.3           **TPM**   9.18              10.69       0.86       **TPM**

  1965          JJA          1.0         77.6            79.0        -1.4           -0.7      8.59              9.83        0.87       0.96

  1965          JAS          1.2         77.2            77.5        -0.3           -0.7      10.87             9.45        1.15       1.01\*

  1965          ASO          1.4         70.7            71.1        -0.4           0.0       8.12              8.05        1.01       1.01\*

  1965          SON          1.5         61.7            60.9        0.8            0.6       7.41              8.47        0.87       0.74

  1965          OND          1.6         52.0            50.5        1.5            0.7       3.40              9.79        0.35       0.58

  1965          NDJ          1.5         42.9            43.2        -0.3           -0.2      6.76              12.96       0.52       0.49

  1966          DJF          1.2         39.4            41.1        -1.7           -1.5      8.57              14.19       0.60       0.57

  1966          JFM          1.1         41.3            43.7        -2.4           -1.4      8.95              15.19       0.59       0.65

  1966          FMA          0.8         50.3            50.4        -0.1           -1.2      10.10             13.44       0.75       0.72

  1966          MAM          0.5         58.1            59.1        -1.0                     10.46             12.65       0.83        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table5 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 8. El                                                                                                                        
  Niño                                                                                                                                 
  1968-1969**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1968          OND          0.6         48.8            50.5        -1.7           **TPM**   12.89             9.79        1.32       **TPM**

  1968          NDJ          0.9         41.2            43.2        -2.0           -2.2      13.93             12.96       1.07       1.10

  1969          DJF          1.0         38.3            41.1        -2.8           -2.9      13.02             14.19       0.92       0.92

  1969          JFM          1.0         39.8            43.7        -3.9           -3.1      11.56             15.19       0.76       0.87

  1969          FMA          0.9         47.8            50.4        -2.6           -2.7      12.63             13.44       0.94       0.91

  1969          MAM          0.7         57.4            59.1        -1.7           -1.3      12.96             12.65       1.02       1.01

  1969          AMJ          0.6         69.0            68.5        0.5                      14.18             13.08       1.08        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table6 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 9. El                                                                                                                        
  Niño                                                                                                                                 
  1969-1970**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1969          ASO          0.6         69.8            71.1        -1.3           **TPM**   6.34              8.05        0.79       **TPM**

  1969          SON          0.7         59.3            60.9        -1.6           -1.8      5.90              8.47        0.70       0.70

  1969          OND          0.7         48.1            50.5        -2.4           -2.9      11.87             9.79        1.21       0.92

  1969          NDJ          0.6         38.6            43.2        -4.6           -4.1      11.02             12.96       0.85       1.00

  1970          DJF          0.5         35.9            41.1        -5.2                     13.55             14.19       0.95        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table7 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 10.                                                                                                                          
  El Niño                                                                                                                              
  1972-1973**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1941-\     from\                    during\           (1941-\     of\        
                                         Period**        1970)**     Normal**                 Period**          1970)**     Total to\  
                                                                                                                            Normal**   

  1972          AMJ          0.5         66.9            68.4        -1.5           **TPM**   9.64              11.59       0.83       **TPM**

  1972          MJJ          0.8         72.5            74.9        -2.4           -2.1      12.46             11.31       1.10       1.07

  1972          JJA          1.1         75.8            78.3        -2.5           -1.7      13.24             10.45       1.27       1.26

  1972          JAS          1.3         76.7            76.8        -0.1           -0.7      14.41             10.16       1.42       1.37

  1972          ASO          1.5         71.0            70.5        0.5            0.3       12.07             8.49        1.42       1.44

  1972          SON          1.8         61.0            60.4        0.6            0.4\*     12.99             8.71        1.49       1.55\*

  1972          OND          2.0         50.1            49.9        0.2            0.4\*     17.42             10.07       1.73       1.51

  1972          NDJ          2.1         42.6            42.3        0.3            0.3       16.76             12.66       1.32       1.39

  1973          DJF          1.8         40.2            39.9        0.3            0.9       15.17             13.63       1.11       1.31

  1973          JFM          1.2         44.9            42.7        2.2            1.2       16.91             14.18       1.19       1.27

  1973          FMA          0.5         51.2            50.1        1.1                      20.51             13.54       1.51        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table8 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 11.                                                                                                                          
  El Niño                                                                                                                              
  1976-1977**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1941-\     from\                    during\           (1941-\     of\        
                                         Period**        1970)**     Normal**                 Period**          1970)**     Total to\  
                                                                                                                            Normal**   

  1976          ASO          0.5         65.0            70.5        -5.5           **TPM**   18.30             8.49        2.16       **TPM**

  1976          SON          0.7         53.8            60.4        -6.6           -6.1      11.55             8.71        1.33       1.44

  1976          OND          0.8         43.8            49.9        -6.1           -7.0      8.28              10.07       0.82       0.87

  1976          NDJ          0.8         33.9            42.3        -8.4           -6.9      5.64              12.66       0.45       0.61

  1977          DJF          0.6         33.6            39.9        -6.3           -5.9      7.61              13.63       0.56       0.61

  1977          JFM          0.5         39.6            42.7        -3.1                     11.63             14.18       0.82        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table9 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 12.                                                                                                                          
  El Niño                                                                                                                              
  1977-1978**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1941-\     from\                    during\           (1941-\     of\        
                                         Period**        1970)**     Normal**                 Period**          1970)**     Total to\  
                                                                                                                            Normal**   

  1977          ASO          0.5         70.1            70.5        -0.4           **TPM**   13.91             8.49        1.64       **TPM**

  1977          SON          0.7         60.5            60.4        0.1            -0.5      15.22             8.71        1.75       1.61

  1977          OND          0.8         48.7            49.9        -1.2           -1.5      14.43             10.07       1.43       1.49

  1977          NDJ          0.8         38.8            42.3        -3.5           -4.3      16.16             12.66       1.28       1.19

  1978          DJF          0.7         31.8            39.9        -8.1                     11.77             13.63       0.86        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table10 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 13.                                                                                                                          
  El Niño                                                                                                                              
  1982-1983**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1951-\     from\                    during\           (1951-\     of\        
                                         Period**        1980)**     Normal**                 Period**          1980)**     Total to\  
                                                                                                                            Normal**   

  1982          AMJ          0.6         66.3            67.8        -1.5           **TPM**   10.83             12.73       0.85       **TPM**

  1982          MJJ          0.7         74.7            74.4        0.3            -0.9      11.94             12.08       0.99       0.96

  1982          JJA          0.8         76.4            77.9        -1.5           -0.9      11.21             10.92       1.03       1.04

  1982          JAS          1.0         75.2            76.7        -1.5           -1.5\*    12.16             10.93       1.11       1.01

  1982          ASO          1.5         68.9            70.3        -1.4           -0.9      8.60              9.69        0.89       0.97

  1982          SON          1.9         60.7            60.4        0.3            0.9       9.01              9.81        0.92       0.97

  1982          OND          2.2         53.6            49.9        3.7            2.7       12.14             10.73       1.13       1.02\*

  1982          NDJ          2.3         46.1            42.1        4.0            3.8       12.79             12.64       1.01       1.01

  1983          DJF          2.3         43.2            39.4        3.8            3.2       11.85             13.15       0.90       0.85

  1983          JFM          2.0         43.9            42.2        1.7            1.6       8.93              14.10       0.63       0.82

  1983          FMA          1.6         49.3            49.9        -0.6           -0.4      13.17             14.08       0.94       1.01

  1983          MAM          1.2         56.5            58.9        -2.4           -2.0      21.28             14.61       1.46       1.37

  1983          AMJ          1.0         64.9            67.8        -2.9           -2.0      21.77             12.73       1.71       1.51

  1983          MJJ          0.6         73.6            74.4        -0.8                     16.68             12.08       1.38        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table11 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 14.                                                                                                                          
  El Niño                                                                                                                              
  1986-1988**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1951-\     from\                    during\           (1951-\     of\        
                                         Period**        1980)**     Normal**                 Period**          1980)**     Total to\  
                                                                                                                            Normal**   

  1986          JAS          0.5         78.0            76.7        1.3            **TPM**   6.34              10.93       0.58       **TPM**

  1986          ASO          0.7         70.8            70.3        0.5            1.1       7.76              9.69        0.80       0.86

  1986          SON          0.9         61.9            60.4        1.5            0.8       11.81             9.81        1.20       1.07

  1986          OND          1.1         50.2            49.9        0.3            0.5       12.93             10.73       1.21       1.13\*

  1986          NDJ          1.2         41.9            42.1        -0.2           0.1\*     12.35             12.64       0.98       0.98

  1987          DJF          1.3         39.6            39.4        0.2            0.5       9.79              13.15       0.74       0.75

  1987          JFM          1.2         43.7            42.2        1.5            0.9       7.66              14.10       0.54       0.59

  1987          FMA          1.1         51.0            49.9        1.1            1.6       7.08              14.08       0.50       0.50

  1987          MAM          1.0         61.0            58.9        2.1            1.6       6.62              14.61       0.45       0.53

  1987          AMJ          1.0         69.5            67.8        1.7            2.1\*     8.26              12.73       0.65       0.64

  1987          MJJ          1.2         77.0            74.4        2.6            2.0       9.79              12.08       0.81       0.67\*

  1987          JJA          1.5         79.6            77.9        1.7            1.8       6.11              10.92       0.56       0.62

  1987          JAS          1.6         77.9            76.7        1.2            0.6       5.24              10.93       0.48       0.45

  1987          ASO          1.6         69.2            70.3        -1.1           -0.2      2.89              9.69        0.30       0.45

  1987          SON          1.5         59.6            60.4        -0.8           -0.5      5.56              9.81        0.57       0.57

  1987          OND          1.3         50.3            49.9        0.4            0.3       9.07              10.73       0.85       0.81

  1987          NDJ          1.1         43.5            42.1        1.4            0.5       12.59             12.64       1.00       0.90

  1988          DJF          0.8         39.0            39.4        -0.4           -0.1      11.21             13.15       0.85       0.80

  1988          JFM          0.5         40.8            42.2        -1.4                     7.93              14.10       0.56        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table12 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 15.                                                                                                                          
  El Niño                                                                                                                              
  1991-1992**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1961-\     from\                    during\           (1961-\     of\        
                                         Period**        1990)**     Normal**                 Period**          1990)**     Total to\  
                                                                                                                            Normal**   

  1991          AMJ          0.6         72.0            67.5        4.5            **TPM**   10.23             12.82       0.80       **TPM**

  1991          MJJ          0.8         77.8            74.2        3.6            3.2       9.70              12.42       0.78       0.70

  1991          JJA          0.9         79.2            77.7        1.5            2.0       5.86              11.00       0.53       0.75

  1991          JAS          0.9         77.3            76.5        0.8            0.9       10.08             10.89       0.95       0.89

  1991          ASO          0.8         70.6            70.1        0.5            0.3       11.14             9.54        1.18       1.13

  1991          SON          1.0         60.2            60.7        -0.5           0.2\*     12.22             10.20       1.20       1.22\*

  1991          OND          1.4         51.0            50.3        0.7            0.6       14.02             11.35       1.27       1.17

  1991          NDJ          1.7         43.8            42.1        1.7            2.3       13.11             12.31       1.05       1.13

  1992          DJF          1.8         43.4            39.0        4.4            3.0       12.84             12.00       1.00       0.93

  1992          JFM          1.7         45.3            42.3        3.0            3.0       10.07             12.24       0.75       0.78

  1992          FMA          1.6         51.9            50.2        1.7            1.4       7.87              13.03       0.60       0.65

  1992          MAM          1.4         58.5            59.0        -0.5           -0.1      8.39              14.10       0.61       0.62

  1992          AMJ          1.1         65.9            67.5        -1.6           -1.2      8.20              12.82       0.64       0.77

  1992          MJJ          0.8         72.7            74.2        -1.5                     13.32             12.42       1.05        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table13 .anchor}

  ---------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table                                                                                                                           
  16. El                                                                                                                            
  Niño                                                                                                                              
  1993**                                                                                                                            

  **Year**   **Period**   **SST\      **Temperature                                        **Precipitation                          
                          Anomaly**   Data**                                               Data**                                   

                                      **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                      during\         (1961-\     from\                    during\           (1961-\     of\        
                                      Period**        1990)**     Normal**                 Period**          1990)**     Total to\  
                                                                                                                         Normal**   

  1993       FMA          0.6         47.9            50.2        -2.3           **TPM**   12.16             13.03       0.93       **TPM**

  1993       MAM          0.8         57.1            59.0        -1.9           -1.7      13.33             14.10       0.95       0.97

  1993       AMJ          0.8         66.7            67.5        -0.8           -0.5      13.14             12.82       1.02       1.03

  1993       MJJ          0.7         75.5            74.2        1.3            1.0       13.45             12.42       1.08       1.02

  1993       JJA          0.5         80.1            77.7        2.4                      10.71             11.00       0.97        
  ---------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table14 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 17.                                                                                                                          
  El Niño                                                                                                                              
  1994-1995**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1961-\     from\                    during\           (1961-\     of\        
                                         Period**        1990)**     Normal**                 Period**          1990)**     Total to\  
                                                                                                                            Normal**   

  1994          MAM          0.5         59.0            59.0        0.0            **TPM**   17.04             14.10       1.21       **TPM**

  1994          AMJ          0.6         68.1            67.5        0.6            0.0       17.56             12.82       1.37       1.31

  1994          MJJ          0.6         73.5            74.2        -0.7           0.0       16.66             12.42       1.34       1.45\*

  1994          JJA          0.6         77.9            77.7        0.2            -0.7      17.95             11.00       1.63       1.42

  1994          JAS          0.6         74.9            76.5        -1.6           -0.8\*    14.07             10.89       1.29       1.41

  1994          ASO          0.7         69.0            70.1        -1.1           -0.6      12.56             9.54        1.32       1.25

  1994          SON          0.9         61.5            60.7        0.8            1.0       11.55             10.20       1.13       1.11

  1994          OND          1.2         53.5            50.3        3.2            2.6       10.04             11.35       0.88       1.00

  1994          NDJ          1.3         46.0            42.1        3.9            3.2       12.34             12.31       1.00       0.91

  1995          DJF          1.2         41.4            39.0        2.4            2.7       10.11             12.00       0.84       0.92

  1995          JFM          0.9         44.2            42.3        1.9            2.0       11.29             12.24       0.92       0.83

  1995          FMA          0.7         51.8            50.2        1.6                      9.63              13.03       0.74        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table15 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 18.                                                                                                                          
  El Niño                                                                                                                              
  1997-1998**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1961-\     from\                    during\           (1961-\     of\        
                                         Period**        1990)**     Normal**                 Period**          1990)**     Total to\  
                                                                                                                            Normal**   

  1997          AMJ          0.9         63.2            67.5        -4.3           **TPM**   14.00             12.82       1.09       **TPM**

  1997          MJJ          1.4         71.6            74.2        -2.6           -2.8      14.84             12.42       1.19       1.17

  1997          JJA          1.7         76.2            77.7        -1.5           -1.5      13.44             11.00       1.22       1.19

  1997          JAS          2.0         76.2            76.5        -0.3           -0.8      12.53             10.89       1.15       1.21

  1997          ASO          2.3         69.5            70.1        -0.6           -0.8      11.98             9.54        1.26       1.30\*

  1997          SON          2.4         59.1            60.7        -1.6           -1.4\*    15.05             10.20       1.48       1.25

  1997          OND          2.5         48.3            50.3        -2.0           -0.8      11.49             11.35       1.01       1.17

  1997          NDJ          2.5         43.2            42.1        1.1            1.1       12.46             12.31       1.01       0.95

  1998          DJF          2.4         43.3            39.0        4.3            3.3       9.98              12.00       0.83       0.91

  1998          JFM          2.0         46.7            42.3        4.4            3.2       10.92             12.24       0.89       0.92

  1998          FMA          1.4         51.2            50.2        1.0            2.0       13.55             13.03       1.04       0.97

  1998          MAM          1.1         59.6            59.0        0.6                      13.90             14.10       0.99       
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table16 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 19.                                                                                                                          
  El Niño                                                                                                                              
  2002-2003**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1971-\     from\                    during\           (1971-\     of\        
                                         Period**        2000)**     Normal**                 Period**          2000)**     Total to\  
                                                                                                                            Normal**   

  2002          AMJ          0.7         68.2            66.9        1.3            **TPM**   12.05             13.08       0.93       **TPM**

  2002          MJJ          0.8         74.2            73.8        0.4            1.1       13.38             12.92       1.06       1.04

  2002          JJA          0.9         79.0            77.4        1.6            1.4       12.53             11.86       1.13       1.20

  2002          JAS          0.9         78.4            76.1        2.3            2.1\*     15.06             10.64       1.42       1.34

  2002          ASO          1.1         72.1            69.7        2.4            1.8       13.90             9.74        1.47       1.41\*

  2002          SON          1.3         60.9            60.2        0.7            0.9       13.68             10.19       1.34       1.33

  2002          OND          1.5         49.5            49.9        -0.4           -0.7      13.00             11.86       1.19       1.26

  2002          NDJ          1.3         39.8            42.2        -2.4           -1.7      10.31             12.96       0.82       1.08

  2003          DJF          1.1         37.1            39.5        -2.4           -2.2      15.87             12.20       1.23       0.99

  2003          JFM          0.8         41.0            42.7        -1.7           -1.1      12.36             12.53       0.93       1.11

  2003          FMA          0.6         50.7            50.0        0.7                      15.46             12.49       1.17        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table17 .anchor}

**Appendix 2. Summary of La Niña events and related meteorological
data** []{#table18 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 20.                                                                                                                          
  La Niña                                                                                                                              
  1950-1951**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1911-\     from\                    during\           (1911-\     of\        
                                         Period**        1940)**     Normal**                 Period**          1940)**     Total to\  
                                                                                                                            Normal**   

  1950          DJF          -1.8        45.4            40.4        5.0            **TPM**   27.38             13.09       2.09       **TPM**

  1950          JFM          -1.5        46.6            43.2        3.4            2.4       25.47             14.00       1.82       1.63

  1950          FMA          -1.4        48.8            50.1        -1.3           0.3       13.13             13.37       0.98       1.17

  1950          MAM          -1.4        57.7            58.8        -1.1           -0.9      9.45              13.11       0.72       0.86

  1950          AMJ          -1.4        67.3            67.6        -0.3           -0.5      10.37             12.00       0.86       1.00

  1950          MJJ          -1.2        74.3            74.3        0.0            -0.9      16.54             11.75       1.41       1.31

  1950          JJA          -0.9        75.2            77.5        -2.3           -1.8      19.10             11.59       1.65       1.56

  1950          JAS          -0.8        73.1            76.3        -3.2           -2.1      18.00             11.01       1.63       1.51

  1950          ASO          -0.8        69.3            70.2        -0.9           -1.9      11.90             9.62        1.24       1.38

  1950          SON          -0.8        59.0            60.6        -1.6           -1.8      11.84             9.41        1.26       1.17

  1950          OND          -0.9        47.3            50.3        -3.0           -2.8      10.42             10.19       1.02       1.28

  1950          NDJ          -1.0        39.0            42.8        -3.8           -2.9      19.31             12.46       1.55       1.26

  1951          DJF          -1.0        38.6            40.4        -1.8           -1.7      15.65             13.09       1.20       1.36

  1951          JFM          -0.8        43.8            43.2        0.6            -0.8      18.64             14.00       1.33       1.16

  1951          FMA          -0.6        49.0            50.1        -1.1                     12.85             13.37       0.96        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table19 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 21.                                                                                                                          
  La Niña                                                                                                                              
  1954-1957**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1921-\     from\                    during\           (1921-\     of\        
                                         Period**        1950)**     Normal**                 Period**          1950)**     Total to\  
                                                                                                                            Normal**   

  1954          MAM          -0.5        58.8            59.2        -0.4           **TPM**   12.44             12.75       0.98       **TPM**

  1954          AMJ          -0.7        68.7            68.3        0.4            0.0       10.64             10.66       1.00       0.87

  1954          MJJ          -0.7        75.0            75.0        0.0            1.1       6.93              10.93       0.63       0.70

  1954          JJA          -0.8        81.5            78.6        2.9            2.2       4.74              10.46       0.45       0.58

  1954          JAS          -1.0        81.1            77.3        3.8            3.0       6.60              10.01       0.66       0.71

  1954          ASO          -1.1        73.4            71.2        2.2            2.2       8.82              8.57        1.03       0.88

  1954          SON          -1.1        62.1            61.4        0.7            0.6       8.33              8.67        0.96       0.98

  1954          OND          -1.0        49.8            50.9        -1.1           -0.7      9.62              9.99        0.96       0.85

  1954          NDJ          -1.0        41.9            43.5        -1.6           -1.4      7.94              12.40       0.64       0.88

  1955          DJF          -1.0        39.8            41.2        -1.4           -1.2      13.58             13.15       1.03       0.97

  1955          JFM          -0.9        43.5            44.1        -0.6           -0.1      17.88             14.37       1.24       1.30

  1955          FMA          -0.9        52.4            50.8        1.6            1.3       21.25             13.13       1.62       1.41

  1955          MAM          -1.0        62.0            59.2        2.8            1.7       17.41             12.75       1.37       1.32

  1955          AMJ          -1.1        68.9            68.3        0.6            1.1       10.48             10.66       0.98       1.02

  1955          MJJ          -1.0        75.0            75.0        0.0            0.1       7.62              10.93       0.70       0.84

  1955          JJA          -1.0        78.3            78.6        -0.3           0.8       8.72              10.46       0.83       0.84

  1955          JAS          -1.0        79.9            77.3        2.6            1.1\*     10.04             10.01       1.00       1.01

  1955          ASO          -1.5        72.3            71.2        1.1            1.0       10.32             8.57        1.20       1.12\*

  1955          SON          -1.8        60.8            61.4        -0.6           -0.6      10.08             8.67        1.16       1.02

  1955          OND          -2.1        48.5            50.9        -2.4           -2.0      7.03              9.99        0.70       0.91

  1955          NDJ          -1.7        40.4            43.5        -3.1           -2.0      10.66             12.40       0.86       0.95

  1956          DJF          -1.2        40.6            41.2        -0.6           -1.3      17.00             13.15       1.29       1.18

  1956          JFM          -0.8        44.0            44.1        -0.1           0.0       20.06             14.37       1.40       1.37

  1956          FMA          -0.7        51.4            50.8        0.6            0.1       18.62             13.13       1.42       1.23

  1956          MAM          -0.6        59.1            59.2        -0.1           0.1       11.18             12.75       0.88       1.06

  1956          AMJ          -0.6        68.0            68.3        0.3            0.1       9.52              10.66       0.89       0.81

  1956          MJJ          -0.6        75.8            75.0        0.8            0.3       7.23              10.93       0.66       0.72

  1956          JJA          -0.7        79.1            78.6        0.5            0.5       6.25              10.46       0.60       0.56

  1956          JAS          -0.8        77.5            77.3        0.2            0.4       4.11              10.01       0.41       0.50

  1956          ASO          -0.9        71.7            71.2        0.5            0.1       4.16              8.57        0.49       0.45

  1956          SON          -0.9        61.0            61.4        -0.4           1.1       4.00              8.67        0.46       0.66

  1956          OND          -0.9        54.0            50.9        3.1            1.4       10.25             9.99        1.03       0.97

  1956          NDJ          -0.8        45.1            43.5        1.6            2.8       17.65             12.40       1.42       1.35

  1957          DJF          -0.5        45.0            41.2        3.8                      21.16             13.15       1.61        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 22.                                                                                                                          
  La Niña                                                                                                                              
  1961-1962**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1961          ASO          -0.6        69.8            71.1        -1.3           **TPM**   4.09              8.05        0.51       **TPM**

  1961          SON          -0.6        60.9            60.9        0.0            -0.6      5.34              8.47        0.63       0.77

  1961          OND          -0.5        50.1            50.5        -0.4           -0.6      11.49             9.79        1.17       1.04

  1961          NDJ          -0.5        41.9            43.2        -1.3           -0.7      16.88             12.96       1.30       1.34

  1962          DJF          -0.5        40.6            41.1        -0.5           -1.1      22.08             14.19       1.56       1.42

  1962          JFM          -0.5        42.1            43.7        -1.6           -1.1      21.47             15.19       1.41       1.53

  1962          FMA          -0.5        49.2            50.4        -1.2           -1.0      21.87             13.44       1.63       1.40

  1962          MAM          -0.5        58.8            59.1        -0.3                     14.67             12.65       1.16        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table20 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 23.                                                                                                                          
  La Niña                                                                                                                              
  1964-1965**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1964          MAM          -0.5        60.3            59.1        1.2            **TPM**   14.91             12.65       1.18       **TPM**

  1964          AMJ          -0.7        69.9            68.5        1.4            0.8       12.11             10.71       1.13       1.03

  1964          MJJ          -0.7        75.3            75.4        -0.1           0.0       8.41              10.69       0.79       0.91

  1964          JJA          -0.8        77.8            79.0        -1.2           -1.0      7.93              9.83        0.81       0.86\*

  1964          JAS          -0.9        75.8            77.5        -1.7           -1.9\*    9.37              9.45        0.99       0.97

  1964          ASO          -1.0        68.3            71.1        -2.8           -1.9\*    9.04              8.05        1.12       1.03

  1964          SON          -1.1        59.8            60.9        -1.1           -1.4      8.15              8.47        0.96       1.06

  1964          OND          -1.1        50.3            50.5        -0.2           0.1       10.65             9.79        1.09       0.99

  1964          NDJ          -1.0        44.7            43.2        1.5            0.3       11.80             12.96       0.91       0.97

  1965          DJF          -0.8        40.8            41.1        -0.3           -0.6      12.84             14.19       0.90       0.91

  1965          JFM          -0.5        40.6            43.7        -3.1                     13.82             15.19       0.91        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table21 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 24.                                                                                                                          
  La Niña                                                                                                                              
  1967-1968**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1931-\     from\                    during\           (1931-\     of\        
                                         Period**        1960)**     Normal**                 Period**          1960)**     Total to\  
                                                                                                                            Normal**   

  1967          SON          -0.5        56.8            60.9        -4.1           **TPM**   7.37              8.47        0.87       **TPM**

  1967          OND          -0.5        48.8            50.5        -1.7           -2.9      11.32             9.79        1.16       1.02

  1967          NDJ          -0.6        40.2            43.2        -3.0           -3.1      13.25             12.96       1.02       0.96

  1968          DJF          -0.7        36.4            41.1        -4.7           -4.4      10.02             14.19       0.71       0.77

  1968          JFM          -0.9        38.2            43.7        -5.5           -4.7      8.61              15.19       0.57       0.64

  1968          FMA          -0.8        46.5            50.4        -3.9           -3.6      8.68              13.44       0.65       0.78

  1968          MAM          -0.8        57.6            59.1        -1.5                     14.32             12.65       1.13        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table22 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 25.                                                                                                                          
  La Niña                                                                                                                              
  1970-1972**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1941-\     from\                    during\           (1941-\     of\        
                                         Period**        1970)**     Normal**                 Period**          1970)**     Total to\  
                                                                                                                            Normal**   

  1970          JJA          -0.6        76.7            78.3        -1.6           **TPM**   13.33             10.45       1.28       **TPM**

  1970          JAS          -0.8        77.8            76.8        1.0            0.4       9.36              10.16       0.92       1.07

  1970          ASO          -0.8        72.3            70.5        1.8            1.4\*     8.69              8.49        1.02       0.95

  1970          SON          -0.8        61.7            60.4        1.3            1.3       7.90              8.71        0.91       0.93

  1970          OND          -0.9        50.6            49.9        0.7            0.6       8.74              10.07       0.87       0.81

  1970          NDJ          -1.2        42.0            42.3        -0.3           -0.1      8.46              12.66       0.67       0.78

  1971          DJF          -1.4        39.2            39.9        -0.7           -1.4      10.96             13.63       0.80       0.73

  1971          JFM          -1.4        39.6            42.7        -3.1           -2.2      10.31             14.18       0.73       0.78

  1971          FMA          -1.2        47.2            50.1        -2.9           -3.3      10.99             13.54       0.81       0.75

  1971          MAM          -1.0        55.2            59.1        -3.9           -3.0      9.22              13.21       0.70       0.78

  1971          AMJ          -0.8        66.2            68.4        -2.2           -2.8      9.74              11.59       0.84       0.85

  1971          MJJ          -0.8        72.5            74.9        -2.4           -2.0      11.40             11.31       1.01       1.07

  1971          JJA          -0.8        76.9            78.3        -1.4           -1.6      14.34             10.45       1.37       1.22

  1971          JAS          -0.8        75.9            76.8        -0.9           -0.1      12.98             10.16       1.28       1.25

  1971          ASO          -0.9        72.5            70.5        2.0            1.5       9.25              8.49        1.09       0.96

  1971          SON          -0.9        63.7            60.4        3.3            3.6       4.56              8.71        0.52       0.79

  1971          OND          -1.0        55.3            49.9        5.4            4.4       7.62              10.07       0.76       0.73

  1971          NDJ          -0.9        46.9            42.3        4.6            4.8       11.50             12.66       0.91       0.89

  1972          DJF          -0.7        44.3            39.9        4.4                      13.77             13.63       1.01        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table23 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 26.                                                                                                                          
  La Niña                                                                                                                              
  1973-1974**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1971-\     from\                    during\           (1941-\     of\        
                                         Period**        2000)**     Normal**                 Period**          1970)**     Total to\  
                                                                                                                            Normal**   

  1973          AMJ          -0.5        65.5            68.4        -2.9           **TPM**   17.52             11.59       1.51       **TPM**

  1973          MJJ          -0.8        72.9            74.9        -2.0           -1.9      18.00             11.31       1.59       1.49

  1973          JJA          -1.1        77.6            78.3        -0.7           -0.6      14.26             10.45       1.36       1.35

  1973          JAS          -1.3        77.7            76.8        0.9            1.1       11.02             10.16       1.08       1.08

  1973          ASO          -1.4        73.5            70.5        3.0            3.1       6.67              8.49        0.79       1.11

  1973          SON          -1.7        65.7            60.4        5.3            4.1       12.66             8.71        1.45       1.22

  1973          OND          -1.9        53.8            49.9        3.9            4.6\*     14.33             10.07       1.42       1.50\*

  1973          NDJ          -2.0        46.8            42.3        4.5            3.7       20.46             12.66       1.62       1.40

  1974          DJF          -1.8        42.6            39.9        2.7            4.0       15.69             13.63       1.15       1.34

  1974          JFM          -1.6        47.5            42.7        4.8            3.1       17.71             14.18       1.25       1.10

  1974          FMA          -1.2        52.0            50.1        1.9            2.9       12.23             13.54       0.90       1.08

  1974          MAM          -1.1        61.2            59.1        2.1            0.8       14.26             13.21       1.08       1.12

  1974          AMJ          -0.9        66.7            68.4        -1.7           -0.5      15.81             11.59       1.36       1.23

  1974          MJJ          -0.7        73.1            74.9        -1.8           -2.0      13.94             11.31       1.23       1.28

  1974          JJA          -0.5        75.7            78.3        -2.6                     13.03             10.45       1.25        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table24 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 27.                                                                                                                          
  La Niña                                                                                                                              
  1974-1976**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1941-\     from\                    during\           (1941-\     of\        
                                         Period**        1970)**     Normal**                 Period**          1970)**     Total to\  
                                                                                                                            Normal**   

  1974          ASO          -0.5        68.2            70.5        -2.3           **TPM**   16.04             8.49        1.89       **TPM**

  1974          SON          -0.7        59.0            60.4        -1.4           -1.0      18.14             8.71        2.08       1.67

  1974          OND          -0.8        50.7            49.9        0.8            0.8       10.51             10.07       1.04       1.40

  1974          NDJ          -0.7        45.3            42.3        3.0            2.5       13.71             12.66       1.08       1.02

  1975          DJF          -0.6        43.5            39.9        3.6            3.0       12.70             13.63       0.93       1.19

  1975          JFM          -0.6        45.1            42.7        2.4            2.0       22.24             14.18       1.57       1.35

  1975          FMA          -0.7        50.2            50.1        0.1            0.7       21.12             13.54       1.56       1.61

  1975          MAM          -0.8        58.7            59.1        -0.4           -0.1      22.42             13.21       1.70       1.44

  1975          AMJ          -1.0        68.3            68.4        -0.1           -0.2      12.29             11.59       1.06       1.26

  1975          MJJ          -1.1        74.9            74.9        0.0            -0.2      11.70             11.31       1.03       1.01

  1975          JJA          -1.3        77.8            78.3        -0.5           -0.7      9.87              10.45       0.94       1.09

  1975          JAS          -1.4        75.2            76.8        -1.6           -0.9\*    13.07             10.16       1.29       1.37

  1975          ASO          -1.6        69.8            70.5        -0.7           -0.6      15.97             8.49        1.88       1.60\*

  1975          SON          -1.6        60.8            60.4        0.4            0.7       14.28             8.71        1.64       1.60\*

  1975          OND          -1.7        52.4            49.9        2.5            1.5       12.98             10.07       1.29       1.27

  1975          NDJ          -1.8        43.8            42.3        1.5            2.4       11.23             12.66       0.89       0.98

  1976          DJF          -1.6        43.2            39.9        3.3            3.2       10.51             13.63       0.77       0.83

  1976          JFM          -1.2        47.6            42.7        4.9            4.5       11.71             14.18       0.83       0.76

  1976          FMA          -0.9        55.5            50.1        5.4            3.7       9.13              13.54       0.67       0.83

  1976          MAM          -0.7        59.9            59.1        0.8            1.2       13.04             13.21       0.99       0.91

  1976          AMJ          -0.5        65.7            68.4        -2.7                     12.44             11.59       1.07        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table25 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 28.                                                                                                                          
  La Niña                                                                                                                              
  1983-1984**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1951-\     from\                    during\           (1951-\     of\        
                                         Period**        1980)**     Normal**                 Period**          1980)**     Total to\  
                                                                                                                            Normal**   

  1983          ASO          -0.5        73.1            70.3        2.8            **TPM**   4.58              9.69        0.47       **TPM**

  1983          SON          -0.8        62.0            60.4        1.6            1.1       10.20             9.81        1.04       1.05

  1983          OND          -0.9        48.7            49.9        -1.2           -1.1      17.50             10.73       1.63       1.33

  1983          NDJ          -0.8        38.5            42.1        -3.6           -2.6      16.52             12.64       1.31       1.28

  1984          DJF          -0.5        36.3            39.4        -3.1                     11.92             13.15       0.91        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table26 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 29.                                                                                                                          
  La Niña                                                                                                                              
  1984-1985**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1951-\     from\                    during\           (1951-\     of\        
                                         Period**        1980)**     Normal**                 Period**          1980)**     Total to\  
                                                                                                                            Normal**   

  1984          SON          -0.6        60.4            60.4        0.0            **TPM**   13.17             9.81        1.29       **TPM**

  1984          OND          -1.0        54.2            49.9        4.3            1.1       14.58             10.73       1.32       1.21

  1984          NDJ          -1.1        41.1            42.1        -1.0           0.6       11.60             12.64       0.93       0.98

  1985          DJF          -1.0        38.0            39.4        -1.4           -1.8      8.70              13.15       0.67       0.74

  1985          JFM          -0.8        39.2            42.2        -3.0           -1.2      9.02              14.10       0.68       0.64

  1985          FMA          -0.8        50.8            49.9        0.9            0.0       8.91              14.08       0.68       0.61

  1985          MAM          -0.8        61.1            58.9        2.2            1.3       8.26              14.61       0.60       0.59

  1985          AMJ          -0.7        68.6            67.8        0.8            1.1       7.09              12.73       0.55       0.54

  1985          MJJ          -0.5        74.7            74.4        0.3                      6.18              12.08       0.49        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table27 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 30.                                                                                                                          
  La Niña                                                                                                                              
  1988-1989**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1951-\     from\                    during\           (1951-\     of\        
                                         Period**        1980)**     Normal**                 Period**          1980)**     Total to\  
                                                                                                                            Normal**   

  1988          AMJ          -0.8        67.2            67.8        -0.6           **TPM**   4.40              12.73       0.35       **TPM**

  1988          MJJ          -1.2        75.3            74.4        0.9            0.9       5.57              12.08       0.46       0.46

  1988          JJA          -1.2        80.2            77.9        2.3            1.7       6.10              10.92       0.56       0.59

  1988          JAS          -1.1        78.7            76.7        2.0            1.2       8.10              10.93       0.74       0.65

  1988          ASO          -1.3        69.6            70.3        -0.7           0.1       6.38              9.69        0.66       0.79

  1988          SON          -1.6        59.3            60.4        -1.1           -0.8\*    9.48              9.81        0.97       0.88

  1988          OND          -1.9        49.2            49.9        -0.7           0.7       10.98             10.73       1.02       1.03

  1988          NDJ          -1.9        46.1            42.1        4.0            2.0       13.96             12.64       1.10       1.66

  1989          DJF          -1.7        42.2            39.4        2.8            3.4       17.83             13.15       1.36       1.27

  1989          JFM          -1.5        45.7            42.2        3.5            2.3       19.00             14.10       1.35       1.31

  1989          FMA          -1.1        50.6            49.9        0.7            1.5       17.35             14.08       1.23       1.15

  1989          MAM          -0.9        59.2            58.9        0.3            -0.1      12.60             14.61       0.86       1.10

  1989          AMJ          -0.6        66.5            67.8        -1.3                     15.16             12.73       1.19        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table28 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 31.                                                                                                                          
  La Niña                                                                                                                              
  1995-1996**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1961-\     from\                    during\           (1961-\     of\        
                                         Period**        1990)**     Normal**                 Period**          1990)**     Total to\  
                                                                                                                            Normal**   

  1995          ASO          -0.5        71.3            70.1        1.2            **TPM**   11.14             9.54        1.17       **TPM**

  1995          SON          -0.6        58.2            60.7        -2.5           -1.2      12.22             10.20       1.20       1.20

  1995          OND          -0.7        47.9            50.3        -2.4           -2.4\*    14.02             11.35       1.24       1.17

  1995          NDJ          -0.8        39.9            42.1        -2.2           -1.6      13.11             12.31       1.06       1.12

  1996          DJF          -0.8        38.8            39.0        -0.2           -1.4      12.84             12.00       1.07       0.99

  1996          JFM          -0.7        40.5            42.3        -1.8           -1.7      10.07             12.24       0.82       0.83

  1996          FMA          -0.5        47.0            50.2        -3.2                     7.87              13.03       0.60        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table29 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 32.                                                                                                                          
  La Niña                                                                                                                              
  1998-2000**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1961-\     from\                    during\           (1961-\     of\        
                                         Period**        1990)**     Normal**                 Period**          1990)**     Total to\  
                                                                                                                            Normal**   

  1998          JJA          -0.8        78.8            77.7        1.1            **TPM**   19.51             11.00       1.77       **TPM**

  1998          JAS          -1.0        78.6            76.5        2.1            2.1       8.95              10.89       0.82       1.07

  1998          ASO          -1.1        73.2            70.1        3.1            2.9       5.91              9.54        0.62       0.62\*

  1998          SON          -1.1        64.3            60.7        3.6            3.1       4.28              10.20       0.42       0.62\*

  1998          OND          -1.3        52.9            50.3        2.6            3.3       9.42              11.35       0.83       0.88

  1998          NDJ          -1.5        45.9            42.1        3.8            3.7\*     17.11             12.31       1.39       1.24

  1999          DJF          -1.6        43.7            39.0        4.7            3.6       18.14             12.00       1.51       1.40

  1999          JFM          -1.2        44.6            42.3        2.3            2.7       15.88             12.24       1.30       1.16

  1999          FMA          -0.9        51.4            50.2        1.2            1.0       8.89              13.03       0.68       0.92

  1999          MAM          -0.7        58.5            59.0        -0.5           0.7       10.91             14.10       0.77       0.75

  1999          AMJ          -0.8        68.9            67.5        1.4            0.7       10.20             12.82       0.80       0.82

  1999          MJJ          -0.8        75.3            74.2        1.1            1.4       11.10             12.42       0.89       0.86\*

  1999          JJA          -0.9        79.3            77.7        1.6            1.3       9.80              11.00       0.89       0.85

  1999          JAS          -0.9        77.8            76.5        1.3            1.1       8.21              10.89       0.75       0.79

  1999          ASO          -1.0        70.4            70.1        0.3            0.9\*     7.06              9.54        0.74       0.73

  1999          SON          -1.2        61.9            60.7        1.2            1.2       7.00              10.20       0.69       0.70

  1999          OND          -1.4        52.5            50.3        2.2            2.3       7.53              11.35       0.66       0.69\*

  1999          NDJ          -1.6        45.5            42.1        3.4            3.2       9.01              12.31       0.73       0.74

  2000          DJF          -1.6        43.1            39.0        4.1            3.8       9.77              12.00       0.81       0.80

  2000          JFM          -1.5        46.3            42.3        4.0            3.4       10.61             12.24       0.87       0.90

  2000          FMA          -1.1        52.2            50.2        2.0            2.3       13.32             13.03       1.02       1.04

  2000          MAM          -0.9        59.9            59.0        0.9            1.0       17.23             14.10       1.22       1.15

  2000          AMJ          -0.7        67.6            67.5        0.1            0.8       15.63             12.82       1.22       1.13

  2000          MJJ          -0.6        75.5            74.2        1.3                      11.65             12.42       0.94        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table30 .anchor}

  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------
  **Table 33.                                                                                                                          
  La Niña                                                                                                                              
  2000-2001**                                                                                                                          

  **Year**      **Period**   **SST\      **Temperature                                        **Precipitation                          
                             Anomaly**   Data**                                               Data**                                   

                                         **Average\      **Normal\   **Departure\             **Total\          **Normal\   **Ratio    
                                         during\         (1961-\     from\                    during\           (1961-\     of\        
                                         Period**        1990)**     Normal**                 Period**          1990)**     Total to\  
                                                                                                                            Normal**   

  2000          SON          -0.5        61.1            60.7        0.4            **TPM**   8.55              10.20       0.84       **TPM**

  2000          OND          -0.7        47.5            50.3        -2.8           -2.2      10.09             11.35       0.89       0.93

  2000          NDJ          -0.7        37.9            42.1        -4.2           -3.1      13.04             12.31       1.06       1.07

  2001          DJF          -0.7        36.7            39.0        -2.3           -2.4      15.19             12.00       1.27       1.17

  2001          JFM          -0.5        41.7            42.3        -0.6                     14.48             12.24       1.18        
  ------------- ------------ ----------- --------------- ----------- -------------- --------- ----------------- ----------- ---------- ---------

[]{#table31 .anchor}

**Appendix 3. Methodology for determining \"prevailing short-term
climate\" and \"short-term climate trend\"**

Using average temperature departure and average precipitation departure
for PL~avg~ (as determined from the three-month ONI index periods in
Appendices I & II), along with representative thirty-year climatological
normals and a climatic trend of 5 years in length (centered at the year
of the SST maximum), the following values were calculated for each ENSO
event and included in Tables 3a and 3b:

1\) characteristics of the prevailing short-term climate,

2\) the short-term climate trend (\"∆T\" for temperature trend and
\"∆P\" for precipitation trend), and

3\) departure of the observed from normal.

Other definitions of terms pertinent to Tables 3a and 3b include:

*Event*: Individual El Niño/La Niña cycle described in more detail in
Appendices
[1](http://www.srh.noaa.gov/ohx/research/el_nino/appendix1.htm) &
[2](#appendix2).

*Periods*: Number of three-month periods where SST anomaly departure
from normal is [\>]{.underline}0.5^o^.

*Maximum SST Anomaly*: The maximum SST anomaly observed during the
event.

[TEMPERATURE CHARACTERISTICS]{.underline}

*Average observed departure from normal* (highlighted in red in
Appendices
[1](http://www.srh.noaa.gov/ohx/research/el_nino/appendix1.htm) &
[2](#appendix2)) is computed using PL~avg~: the five periods centered on
the maximum SST anomaly.

*Prevailing short-term climate* is based on a comparison between the
five-year running mean annual temperature for the year during which the
maximum SST anomaly occurred, and the thirty-year climatological normal.
After determining the standard deviation for the Nashville temperature
data for each El Niño/La Niña (Figures 5 & 6), a determination was made
as to which departure from normal should represent \"very warm\" and
\"very cool\" conditions. A departure greater than one standard
deviation (SD) was chosen as that threshold, and SD's were then
calculated separately for El Niño and La Niña events. Departures from
normal of one-half SD or less are considered "near normal." Departures
from normal greater than one-half SD, but no more than one SD, are
considered either "cool" or "warm," depending on the sign. Based on
these SD calculations, the following terms used in the tables are
defined for the El Niño cases:

\"Near normal\" implies a departure from normal of 0.8 ^o^ to -0.8^o^.\
\"Cool\" implies a departure from normal of -0.9^o^ to -1.7^o^.\
\"Very cool\" implies a departure from normal greater than -1.7^o^.\
\"Warm\" implies a departure from normal of 0.9^o^ to 1.7^o^.\
\"Very warm\" implies a departure from normal greater than 1.7^o^.

Similarly, the following terms used in the tables are defined for the La
Niña cases:

> \"Near normal\" implies a departure from normal of 0.6 ^o^ to
> -0.6^o^.\
> \"Cool\" implies a departure from normal of -0.7^o^ to -1.2^o^.\
> \"Very cool\" implies a departure from normal greater than -1.2^o^.\
> \"Warm\" implies a departure from normal of 0.7^o^ to 1.2^o^.\
> \"Very warm\" implies a departure from normal greater than 1.2^o^.

For purposes of segregating the temperature departure data into
categories for \"large\" departures and \"small\" departures, the use of
standard deviation provides an objective threshold. After studying
graphs of the data (Figures 5 & 6), it was determined that this
threshold would effectively segregate the two primary data clusters.
Using this threshold, nine El Niño cycles were determined to be
associated with \"large\" departures from normal and the remaining seven
were associated with small departures. Similarly, nine La Niña cycles
were determined to be associated with \"large\" departures from normal
and the remaining six were associated with small departures. Note that
in Figures 5 & 6, the absolute value of each El Niño/La Niña average
observed departure from normal (taken from Tables 3a & 3b) was plotted
along the Y-axis. The X-axis values (labeled with each plot) indicate
each ENSO event.

*General trend in short-term climate* (∆T) is the difference between the
five-year running mean annual temperature value two years following the
year in which the maximum SST anomaly occurred and that two years prior.
In order to maintain consistency, the aforementioned SD thresholds were
used to define the following terms. For the El Niño cases, those terms
are:

\"Stable\" implies a change of 0.8^o^ to -0.8^o^.\
\"Cooling\" implies a change of -0.9^o^ to -1.7^o^.\
\"Significant cooling\" implies a change greater than -1.7^o^.\
\"Warming\" implies a change of 0.9^o^ to 1.7^o^.\
\"Significant warming\" implies a change greater than 1.7^o^.

And for the La Niña cases, those terms are:

> \"Stable\" implies a change of 0.6^o^ to -0.6^o^.\
> \"Cooling\" implies a change of -0.7^o^ to -1.2^o^.\
> \"Significant cooling\" implies a change greater than -1.2^o^.\
> \"Warming\" implies a change of 0.7^o^ to 1.2^o^.\
> \"Significant warming\" implies a change greater than 1.2^o^.

[PRECIPITATION CHARACTERISTICS]{.underline}

Following is an explanation of the terms used in Table 3a and 3b that
pertains to precipitation:

*Ratio of observed precipitation to normal* is computed using PL~avg~:
centered on the maximum SST anomaly (highlighted in green in Appendices
[1](http://www.srh.noaa.gov/ohx/research/el_nino/appendix1.htm) &
[2](#appendix2)).

*Prevailing short-term climate* is based on the five-year running mean
annual precipitation for the year during which the maximum SST anomaly
occurred compared to the thirty-year climatological normal. After
determining the standard deviation for the Nashville precipitation data
for each El Niño/La Niña (Figures 7 & 8), a determination was made as to
which departure from normal should represent \"very wet\" and \"very
dry\" conditions. As with temperature characteristics, the standard
deviation of the absolute value of the average departure from normal
were calculated separately for El Niño and La Niña cases. A departure
greater than one SD was selected as that threshold. Departures from
normal of one-half SD or less were considered "near normal," and
departures from normal greater than one-half SD, but no more than one
SD, were considered either "dry" or "wet," depending on the sign. The
following terms used in the table are defined for El Niño as follows:

\"Near normal\" implies a departure from normal of 7% to -7%.\
\"Dry\" implies a departure from normal of -8% to -15%.\
\"Very dry\" implies a departure from normal greater than 15%.\
\"Wet\" implies a departure from normal of 8% to 15%.\
\"Very wet\" implies a departure from normal greater than 15%.

Likewise, the following terms used in the table are defined for La Niña
as follows:

> \"Near normal\" implies a departure from normal of 8% to -8%.\
> \"Dry\" implies a departure from normal of -9% to -17%.\
> \"Very dry\" implies a departure from normal greater than 17%.\
> \"Wet\" implies a departure from normal of 9% to 17%.\
> \"Very wet\" implies a departure from normal greater than 17%.

For purposes of segregating the precipitation departure data into
categories for \"large\" departures and \"small\" departures, the use of
standard deviation provides an objective threshold. After studying
graphs of the data (Figures 7 & 8), it was determined that this
threshold would effectively segregate the two primary data clusters.
Using this threshold, seven El Niño cycles were determined to be
associated with \"large\" departures from normal and the remaining nine
were associated with small departures. Similarly, six La Niña cycles
were determined to be associated with \"large\" departures from normal
and the remaining eight were associated with small departures. Note that
in Figures 7 & 8, the absolute value of each El Niño/La Niña average
observed departure from normal (taken from Tables 3a & 3b) was plotted
along the Y-axis. The X-axis values (labeled with each plot) indicate
each ENSO event.

*General trend in short-term climate* (∆T) is the difference between the
five-year running mean annual precipitation two years following the year
in which the maximum SST anomaly occurred and that two years prior. In
order to maintain consistency, the aforementioned SD thresholds were
used to define the following terms. For the El Niño cases, those terms
are:

\"Stable\" implies a change of 7% to -7%.\
\"Decreasing\" implies a change of -8% to -15%.\
\"Rapidly decreasing\" implies a change greater than -15%.\
\"Increasing\" implies a change of 8% to 15%.\
\"Significantly increasing\" implies a change greater than 15%.

And for the La Niña cases, those terms are:

> \"Stable\" implies a change of 8% to -8%.\
> \"Decreasing\" implies a change of -9% to -17%.\
> \"Rapidly decreasing\" implies a change greater than -17%.\
> \"Increasing\" implies a change of 9% to 17%.\
> \"Significantly increasing\" implies a change greater than 17%.

![](media/image11.wmf){width="4.677083333333333in"
height="2.8333333333333335in"}

Figure 5. Standard deviation (1.7^o^) is represented by a dashed grey
line.

![](media/image12.wmf){width="4.6875in" height="2.84375in"}

Figure 6. Standard deviation (1.2^o^) is represented by a dashed grey
line.

![](media/image13.wmf){width="4.6875in" height="2.84375in"}

Figure 7. Standard deviation (15%) is represented by a dashed grey line.

![](media/image14.wmf){width="4.697916666666667in"
height="2.8541666666666665in"}

Figure 8. Standard deviation (17%) is represented by a dashed grey line.

**Appendix 4. Supplemental data pertaining to Section 5.**

**[Summary of El Niño smoothed data (centered on SST
maxima)]{.underline}**

  ---------------------- --------------------------- ---------------------------
  **Table 34. Summary of                             
  El Niño \"pre-SST Max                              
  periods\"**                                        

  **Event**              **Temperature inflection    **Precipitation inflection
                         point**                     point**

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1957-1958](#table3)    2 (maximum)                 3 (maximum)

  [El Niño               N~pre-SST\ Max\ periods~ =  No pre-SST Max inflection
  1963-1964](#table4)    1 (maximum)                 point

  [El Niño               No pre-SST Max inflection   N~pre-SST\ Max\ periods~ =
  1965-1966](#table5)    point                       2.5 (maximum)

  [El Niño               El Niño not sufficiently    
  1968-1969](#table6)    long to verify a pre-SST    
                         Max inflection point        

  [El Niño               El Niño not sufficiently    
  1969-1970](#table7)    long to verify a pre-SST    
                         Max inflection point        

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1972-1973](#table8)    1.5 (maximum)               2 (maximum)

  [El Niño               El Niño not sufficiently    
  1976-1977](#table9)    long to verify a pre-SST    
                         Max inflection point        

  [El Niño               El Niño not sufficiently    
  1977-1978](#table10)   long to verify a pre-SST    
                         Max inflection point        

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1982-1983](#table11)   4 (minimum)                 1 (maximum)

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1986-1988](#table12)   1 (minimum)                 2 (maximum)

                         N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
                         3 (maximum)                 2 (maximum)

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1991-1992](#table13)   3 (minimum)                 3 (maximum)

  [El Niño               El Niño not sufficiently    
  1993](#table14)        long to verify a pre-SST    
                         Max inflection point        

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1994-1995](#table15)   4 (minimum)                 6 (maximum)

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1997-1998](#table16)   1 (maximum)                 2 (maximum)

  [El Niño               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  2002-2003](#table17)   3 (maximum)                 2 (maximum)
  ---------------------- --------------------------- ---------------------------

*[Temperature]{.underline}*

The average number of \"pre-SST Max periods\" = 2 + 1 + 1.5 + 4 + 1 +
3 + 3 + 4 + 1 + 3 / 10 = 2.4.

Dropping the highest and lowest values gives: 2 + 1.5 + 1 + 3 + 3 + 4 +
1 + 3 / 8 = 2.3 periods.

([Note:]{.underline} The highest and lowest values are dropped in order
to eliminate potentially unrepresentative outliers.)

The period encompassing the temperature pattern centered at the SST
maximum was defined as:

PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1

Thus PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1 = 5 periods.

*[Precipitation]{.underline}*

The average number of \"pre-SST Max periods\" = 3 + 2.5 + 2 + 1 + 2 +
2 + 3 + 6 + 2 + 2 / 10 = 2.6.

Dropping the highest and lowest values gives: 3 + 2.5 + 2 + 2 + 2 + 3 +
2 + 2 / 8 = 2.3 periods.

The period encompassing the temperature pattern centered at the SST
maximum was defined as:

PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1

Thus PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1 = 5 periods.

**[Summary of La Niña smoothed data (centered on SST
maxima)]{.underline}**

  ---------------------- --------------------------- ---------------------------
  **Table 35. Summary of                             
  La Niña \"pre-SST Max                              
  periods\"**                                        

  **Event**              **Temperature inflection    **Precipitation inflection
                         point**                     point**

  [La Niña               La Niña not sufficiently    
  1950-1951](#table18)   long to verify a pre-SST    
                         Max inflection point        

  [La Niña               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1954-1957](#table19)   3 (maximum)                 2 (maximum)

  [La Niña               La Niña not sufficiently    
  1961-1962](#table20)   long to verify a pre-SST    
                         Max inflection point        

  [La Niña               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1964-1965](#table21)   1.5 (minimum)               3 (minimum)

  [La Niña               No pre-SST Max inflection   No pre-SST Max inflection
  1967-1968](#table22)   point                       point

  [La Niña               N~pre-SST\ Max\ periods~ =  No pre-SST Max inflection
  1970-1972](#table23)   4 (maximum)                 point

  [La Niña               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1973-1974](#table24)   1 (maximum)                 1 (maximum)

  [La Niña               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1974-1976](#table25)   4 (maximum)                 2.5 (maximum)

  [La Niña               La Niña not sufficiently    
  1983-1984](#table26)   long to verify a pre-SST    
                         Max inflection point        

  [La Niña               La Niña not sufficiently    
  1984-1985](#table27)   long to verify a pre-SST    
                         Max inflection point        

  [La Niña               N~pre-SST\ Max\ periods~ =  No pre-SST Max inflection
  1988-1989](#table28)   1 (minimum)                 point

  [La Niña               N~pre-SST\ Max\ periods~ =  No pre-SST Max inflection
  1995-1996](#table29)   1 (minimum)                 point

  [La Niña               N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
  1998-2000](#table30)   1 (maximum)                 3.5 (minimum)

                         N~pre-SST\ Max\ periods~ =  N~pre-SST\ Max\ periods~ =
                         3 (minimum)                 1 (minimum)

  [La Niña               La Niña not sufficiently    
  2000-2001](#table31)   long to verify a pre-SST    
                         Max inflection point        
  ---------------------- --------------------------- ---------------------------

*[Temperature]{.underline}*

The average number of \"pre-SST Max periods\" = 3 + 1.5 + 4 + 1 + 4 +
1 + 1 + 1 + 3 / 9 = 2.2.

Dropping the highest and lowest values gives: 3 + 1.5 + 1 + 4 + 1 + 1 +
3 / 7 = 2.1 periods.

The period encompassing the temperature pattern centered at the SST
maximum was defined as:

PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1

Thus PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1 = 5 periods.

*[Precipitation]{.underline}*

The average number of \"pre-SST Max periods\" = 2 + 3 + 1 + 2.5 + 3.5 +
1 / 6 = 2.2.

Dropping the highest and lowest values gives: 2 + 3 + 2.5 + 1 / 4 = 2.2
periods.

The period encompassing the temperature pattern centered at the SST
maximum was defined as:

PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1,

Thus PL~avg~ = \[2 x N~pre-SST\ Max\ periods~\] + 1 = 5 periods.

**Appendix 5. Normal temperature and precipitation values for Nashville,
Tennessee used in this study**

  --------- ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------
  ** **     **1911-1940**                                                   **1921-1950**                                                   **1931-1960**                                                   **1941-1970**                                      

            **Temperature**                **Precipitation**                **Temperature**                **Precipitation**                **Temperature**                **Precipitation**                **Temperature**                **Precipitation**   

            **Month**         **Period**   **Month**           **Period**   **Month**         **Period**   **Month**           **Period**   **Month**         **Period**   **Month**           **Period**   **Month**         **Period**   **Month**           **Period**

  **DJF**   38.6              40.4         4.76                13.09        39.9              41.2         4.93                13.15        39.9              41.1         5.49                14.19        38.3              39.9         4.75                13.63

  **JFM**   41.6              43.2         4.13                14.00        42.3              44.1         4.16                14.37        42.0              43.7         4.51                15.19        41.0              42.7         4.43                14.18

  **FMA**   49.2              50.1         5.11                13.37        49.8              50.8         5.28                13.13        49.1              50.4         5.19                13.44        48.7              50.1         5.00                13.54

  **MAM**   59.0              58.8         4.13                13.11        59.7              59.2         3.69                12.75        59.6              59.1         3.74                12.65        60.1              59.1         4.11                13.21

  **AMJ**   68.2              67.6         3.87                12.00        68.2              68.3         3.78                10.66        68.6              68.5         3.72                10.71        68.5              68.4         4.10                11.59

  **MJJ**   75.6              74.3         4.00                11.75        76.9              75.0         3.19                10.93        77.4              75.4         3.25                10.69        76.6              74.9         3.38                11.31

  **JJA**   79.1              77.5         3.88                11.59        80.0              78.6         3.96                10.46        80.2              79.0         3.72                9.83         79.6              78.3         3.83                10.45

  **JAS**   77.8              76.3         3.71                11.01        78.7              77.3         3.31                10.01        79.2              77.5         2.86                9.45         78.5              76.8         3.24                10.16

  **ASO**   72.3              70.3         3.71                9.69         71.8              70.1         3.46                9.54         71.3              69.7         3.59                9.74         71.8              70.2         3.42                9.62

  **SON**   61.0              60.6         2.49                9.41         61.8              61.4         2.52                8.67         61.5              60.9         2.32                8.47         60.9              60.4         2.16                8.71

  **OND**   49.0              50.3         3.50                10.19        49.3              50.9         3.41                9.99         48.5              50.5         3.28                9.79         48.4              49.9         3.46                10.07

  **NDJ**   41.0              42.8         4.20                12.46        41.6              43.5         4.06                12.40        41.4              43.2         4.19                12.96        40.4              42.3         4.45                12.66

  **Yr**    59.3                           47.20                            60.1                           45.03                            60.0                           45.14                            59.4                           46.00                
  --------- ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------

  --------- ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------
  ** **     **1951-1980**                                                   **1961-1990**                                                   **1971-2000**                                      

            **Temperature**                **Precipitation**                **Temperature**                **Precipitation**                **Temperature**                **Precipitation**   

            **Month**         **Period**   **Month**           **Period**   **Month**         **Period**   **Month**           **Period**   **Month**         **Period**   **Month**           **Period**

  **DJF**   37.1              39.4         4.49                13.15        36.2              39.0         3.58                12.00        36.8              39.5         3.97                12.20

  **JFM**   40.4              42.2         4.03                14.10        40.4              42.3         3.81                12.24        41.3              42.8         3.69                12.53

  **FMA**   49.0              49.9         5.58                14.08        50.2              50.2         4.85                13.03        50.1              50.2         4.87                12.49

  **MAM**   59.6              58.9         4.47                14.61        59.2              59.0         4.37                14.10        58.5              58.6         3.93                13.87

  **AMJ**   68.1              67.8         4.56                12.73        67.7              67.5         4.88                12.82        67.1              66.9         5.07                13.08

  **MJJ**   75.8              74.4         3.70                12.08        75.6              74.2         3.57                12.42        75.1              73.8         4.08                12.92

  **JJA**   79.4              77.9         3.82                10.92        79.3              77.7         3.97                11.00        79.1              77.4         3.77                11.13

  **JAS**   78.4              76.7         3.40                10.93        78.1              76.5         3.46                10.89        77.9              76.2         3.28                10.64

  **ASO**   73.2              71.2         2.74                8.57         72.8              71.1         2.87                8.05         72.0              70.5         3.09                8.49

  **SON**   60.2              60.4         2.58                9.81         60.4              60.7         2.62                10.20        59.9              60.2         2.87                10.91

  **OND**   48.6              49.9         3.52                10.73        50.0              50.3         4.12                11.35        49.3              49.9         4.45                11.86

  **NDJ**   40.9              42.1         4.63                12.64        40.5              42.1         4.61                12.31        40.5              42.1         4.54                12.96

  **Yr**    59.2                           48.49                            59.1                           47.30                            58.9                           48.11                
  --------- ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------ ----------------- ------------ ------------------- ------------

Normals for each month and three month-period are given for temperature
and precipitation. For example, in the first row of figures for the
1911-1940 climatological period, the normal mean temperature for January
was 38.6^o^. The normal mean temperature for the three-month period
centered around January (DJF) was 40.4^o^. Likewise, normal
precipitation for January was 4.76 inches. Normal precipitation for the
three-month period centered around January (DJF) was 13.09 inches.