**[2007-2008 Winter Drought Outlook]{.underline}**

**November 2007 Assessment from NOAA's National Weather Service Office
in Raleigh and the North Carolina State Climate Office issued November
29, 2007**

The month of November provided no relief from drought conditions across
central North Carolina as 85 out of 100 counties are now experiencing
extreme to moderate drought. Most of the area received less than a half
inch of rain while just a few locations around the western Triad,
including Winston-Salem and Lexington, received as much as one inch of
rain (Figure 1). In fact, November 2007 was the driest November on
record at the Raleigh-Durham International Airport (RDU), reporting only
0.48" for the entire month. The previous driest November was 0.50" set
in 2001. 2007 November rainfall averaged less than 25 percent of normal
for most of the area (Figure 2), as our normal rainfall for November is
around 3 inches.

![](media/image1.jpeg){width="5.363888888888889in"
height="3.138888888888889in"}

Figure 1: Accumulated Rainfall, Nov 1 -- Nov 29

![](media/image2.jpeg){width="5.354166666666667in" height="3.1625in"}

> Figure 2: Percent of Normal Rainfall, Nov 1 -- Nov 29

As it typical during La Nina patterns in the fall and winter, much of
the heavy rain in November fell to the north and west of the mid
Atlantic states. As much as 3 to 6 inches of rain fell from the Gulf
Coast north across portions of Tennessee and into Pennsylvania, New York
and New England, all bypassing North Carolina and some of the most
drought riddled areas (Figure 3).

![](media/image3.png){width="6.081944444444445in"
height="3.2847222222222223in"}

Figure 3. Observed rainfall across for November 2007.

Through the end of November, there have been only 81 days of measurable
precipitation (0.01" or more) at RDU this year, 11 days less than the
record of 92 days, most recently set in 1969. Similarly, the Piedmont
Triad International Airport (GSO) has reported 76 days of measurable
precipitation through the end of November, 9 days less than the record
of 85 days set in 1986 (Figure 4). Both RDU and GSO are on track to
break the record for the fewest days of measurable precipitation in a
calendar year, even if both locations receive the "normal" 9 days of
measurable precipitation during December. The normal number of days with
measurable rainfall in a year is around 113 for both stations meaning
RDU and GSO have experienced over a months worth of fewer rain days than
normal.

![](media/image4.wmf){width="3.4409722222222223in"
height="2.265972222222222in"}
![](media/image5.wmf){width="3.479861111111111in"
height="2.2416666666666667in"}

Figure 4. Number of days with measurable rain at RDU and GSO.

In addition to a decreased frequency of rainfall both RDU and GSO have
experienced observed monthly rainfall deficits over the last 11 months
(Figure 5). Below normal rainfall has been observed at RDU for 7 of the
last 11 months resulting in a rainfall deficit of nearly 8.50 inches
below normal for the year. At GSO below normal monthly rainfall was
recorded 9 out of the last 11 months with a year to date rainfall
deficit of over 11.50 inches below normal. Year to date rainfall at both
RDU and GSO is currently running as the second driest ever recorded and
given the lack of forecast rainfall for December these records may hold
to the end of the year.

![](media/image6.wmf){width="5.416666666666667in"
height="3.5104166666666665in"}

![](media/image7.wmf){width="5.447916666666667in"
height="3.3645833333333335in"}

Figure 5. Observed rainfall and departures from normal.

Stream Flow and Reservoirs

As of November 29^th^, nearly 90 percent of the stream gages on
unregulated streams in the state were recording flows at or below the
25^th^ percentile, and about 65 percent of the gages were in the 10^th^
percentile (Figure 6).

![](media/image8.jpeg){width="5.043055555555555in"
height="3.240972222222222in"}

Figure 6. Stream flow at long-term stream flow gaging stations. Graphics
courtesy of the USGS.

Of particular note are the very low flows on streams in the headwater
regions of the Cape Fear, Neuse, and Tar Rivers. A number of these
streams are flowing at 1 to 2 percent of normal which translates to very
low inflows into the major water supply reservoirs. For example, inflow
into Falls Lake in Wake County is less than 1 percent of normal and the
inflow into Lake Jordan in Chatham County is 13 percent of normal.

The water supply in Falls Lake has fallen to about 30 percent, which
translates to about a 120 day water supply for the city of Raleigh.
Raleigh has begun to transfer water from smaller reservoirs south of the
city into the Neuse River, which allows more water to be retained in
Falls Lake. This effort will slow the lake's fall and extend the water
supply. In addition the Flat River which runs into Lake Michie, the
water supply reservoir for the city of Durham, currently has a flow near
zero. Lake Michie continues to fall, and is about 14 feet below normal,
which translates to about a 60 day water supply for Durham.

How Drought Conditions Continue to Worsen

The expansion of drought conditions accelerated across North Carolina
during the mid and late summer (Figure 7). Following the hottest and one
of the driest Augusts on record across the state, extreme drought
conditions took hold to nearly the entire state by September. September,
like August set, records as second hottest on record at both RDU and
GSO. Rainfall events have remained sparser than normal through the Fall,
with Central North Carolina experiencing only two significant rain
events since the record-breaking summer. Approximately 70 percent of the
state is currently in either extreme or exceptional drought according to
the latest National Drought Monitor (bottom right image of Figure 7).

![](media/image9.jpeg){width="5.863194444444445in"
height="4.361805555555556in"}

Figure 7 -- Progression of the Drought, August through November.

Precipitation Outlook and La Niña

Looking ahead to this winter, the above normal rainfall needed to end
the drought appears unlikely as moderate La Nina conditions have
developed over the past few weeks. Anomalously cold sea surface
temperature have expanded across the equatorial Pacific (Figure 8) and
several climate models indicate further strengthening to a strong La
Nina is possible. La Niña, the cold phase of the ENSO cycle, occurs when
cooler than normal sea surface temperatures over the central Pacific
Ocean persist for several months. The El Niño/ La Niña phenomena are one
of the main sources of year-to-year variability in weather and climate
for many areas of the United States and even the world.

![](media/image10.png){width="5.43125in" height="2.8819444444444446in"}

Figure 8. Sea surface temperature anomalies. Graphic provided by NOAA's
Climate Prediction Center.

La Niña conditions tend to influence wintertime atmospheric flow across
the eastern North Pacific and North America. La Niña can shift the jet
stream which helps to drive weather systems across North America. During
La Niña the southern stream of the upper level jet, which typically
brings moisture and enhanced storm systems into the mid Atlantic during
the winter months is weakened. At the same time a "blocking" ridge of
high pressure develops over the northern Pacific forcing many storm
systems to remain over the northern half of the U.S as we have seen over
the past month. These factors combine to bring fewer storms and less
moisture to the Carolinas. (Figure 9).

![](media/image11.png){width="4.552777777777778in"
height="2.5409722222222224in"}

Figure 9. La Niña's influence on jet stream provided by NOAA's Climate
Prediction Center.

During La Niña winters, portions of the Pacific Northwest, Midwest and
Northeast experience increased storminess, while southern and eastern
states including North Carolina typically experience less storminess and
precipitation. Along the mid Atlantic there are generally fewer coastal
storms. The displacement of the jet stream due to La Niña results in
fewer coastal storms limiting precipitation. La Niña typically results
in more Alberta Clipper (fast eastward tracking storms across the mid
Atlantic) type winter systems which are drier in nature. The latest
precipitation outlook from NOAA's Climate Prediction Center reflects the
La Niña trend of an increase likelihood of receiving below normal
precipitation across the southeast (Figure 10).

![](media/image12.jpeg){width="4.325694444444444in"
height="2.8305555555555557in"}

Figure 10. Winter precipitation outlook provided by NOAA's Climate
Prediction Center

When the influence of moderate to strong La Niña is combined with
precipitation trends observed over the past 15 years, we find
precipitation typically averages 3 inches below normal during the winter
months for nearly all of Central North Carolina. Given the current
pattern a significant rainfall deficit is expected to continue through
the winter. In contrast a 5 to 7 inch surplus in rainfall is needed this
winter in order to ease the current drought conditions.

A local study of winter precipitation at 5 sites across North Carolina
during 20 past cases of weak, moderate and strong La Niña episodes,
indicates below normal precipitation can be expected 60% of the time
during any La Niña. The occurrence of below normal precipitation
increases to 70% when examining only the moderate and strong La Niña
events. More importantly, central North Carolina has received above
normal precipitation only 1 out of 12 winters (8%) during moderate to
strong La Niña winters (Figure 11).

![](media/image13.png){width="5.8909722222222225in"
height="4.065277777777778in"}

Figure 11. Data provided by the National Climatic Data Center. Graphic
created by the Raleigh National Weather Service Office

Increased Fire Danger...

The drought conditions continue to increased the risk of wildfires. Fall
is one of the peak fire seasons in North Carolina and given the dry
conditions and the amount of dry fuels on the ground. Fuel moisture
values are running low due to the prolonged dry conditions. According to
the Keetch-Byram Drought Index (KBI), designed as a drought index for
fire potential assessment, the state is ranked in a moderate category
for fire danger (Figure 12). Such values of the KBI are often associated
with dry conditions and an increase in dry fuels. During prolonged
severe droughts intense, deep burning fires with significant downwind
spotting can be expected and live fuels are expected to burn actively.
Combining the dry conditions with windy fall days and low humidity
creates a very dangerous fire potential. Fires on such days spread
rapidly becoming extremely dangerous in very little time.

![](media/image14.jpeg){width="4.49375in" height="3.3270833333333334in"}

Figure 12. Keetch-Byran Drought Index. Graphic courtesy of the US Forest
Service. This graphic is updated daily and may be found at:
<http://www.fs.fed.us/land/wfas/kbdi.gif>

Current drought compared to past droughts...

Drought is a naturally occurring extreme in climate variability. Extreme
droughts by definition occur about 4 percent or less of the time through
the climatological record. This means in any given year there is only a
4 percent chance of an extreme drought. Even during extreme droughts,
the impacts can vary based on the duration and time of year. According
to the North Carolina State Climatologist, the drought conditions
through the months of August, September and October reached new levels
not experienced since 1925, surpassing the drought of 2002. By the end
of October and into November North Carolina was experiencing the worst
drought conditions ever recorded going back as far as 1895 when drought
indices were first calculated and archived (Figure 13).

![](media/image15.png){width="4.7347222222222225in"
height="3.2444444444444445in"}

Figure 13. Drought data and graph courtesy of the NC State Climate
office.

Rainfall needed to end the drought...

Based on the current Palmer Drought Severity Index (PDSI), in order to
ameliorate the drought, much of the state still needs 14 to 18 inches of
rain over the next 3 months and 25 to 30 inches over the next 6 months
(Figure 14). These values are 5 to 7 inches above the normal rainfall
expected during an average winter and spring. In the winter, (December
through February), rainfall totals average 9 to 11 inches. When combined
with Spring (December through March), these normal rainfall totals reach
20 to 23 inches. Ameliorating the drought conditions would not bring an
end to the drought impacts on North Carolina, but rather reduce the
exceptional drought conditions to moderate.

Based on climatology, the probability of receiving the 14 to 18 inches
of rainfall necessary to ameliorate the drought over the next 3 months
is approximately 10 to 15 percent. The probability of ameliorating the
drought in 6 months is less than 15 percent.

![](media/image16.png){width="3.3645833333333335in"
height="3.213888888888889in"}![](media/image17.png){width="3.279166666666667in"
height="3.21875in"}

Figure 14. 3 and 6 month rainfall and probabilities calculated data from
the National Climatic Data Center based on rainfall deficits as of
October.

In order to completely end the drought this winter, the state needs as
much as 24 inches of rain over the next 3 months (35 inches over 6
months) and the chances of that occurring are less than 4 percent. The
PDSI is a meteorological drought index which responds to abnormally dry
or wet weather conditions and is calculated based on precipitation and
temperature data, as well as the local available soil moisture. It is
one of many indicators used to determine drought severity. To find out
more about drought indices, access the Raleigh National Weather Service
drought webpage at <http://www.erh.noaa.gov/rah/drought/>

North Carolina stands to miss out on the frequent large scale rain and
snow events necessary to end the drought, leaving the state relatively
dry heading into the growing season and months of increased water needs
next spring (Figure 15).

![](media/image18.png){width="6.404861111111111in"
height="4.784722222222222in"}

Figure 15. Season Drought Outlook provided by NOAA's Climate Prediction
Center

It is possible for above normal precipitation and major snow storms to
occur during La Niña episodes. In the winter of 1973-1974, during a
moderate to strong La Niña, much of the state experienced a
precipitation surplus of 3 to 5 inches. Additionally, the record
breaking snowstorm of January 25, 2000 occurred during a moderate to
strong La Niña phase.

It is important to understand that due to exceptionally low lake levels
and water shortages, even a return to near normal rainfall over the next
three to six months may not bring an end to the current drought. If
climate predictions come to fruition and the rains and snows of the
winter and spring remain below normal, farms, cities and residences will
be facing ongoing water shortages as we move into the summer months next
year. Water shortages of some degree will likely remain into the high
water usage months next summer as demands for water increase with the
heat. With the prospects of a dry winter providing minimal relief from
the current exceptional drought conditions, residents and officials are
urged to examine and develop long term plans to address water
availability, needs and resources.

**Websites**

NC Drought Monitor

[http://www.ncdrought.org](http://www.ncdrought.org/)

State Climate Office of North Carolina

<http://www.nc-climate.ncsu.edu/>

National Weather Service Raleigh, NC

<http://www.erh.noaa.gov/rah/>

Climate Prediction Center

[http://www.cpc.ncep.noaa.gov](http://www.cpc.ncep.noaa.gov/)

**Acknowledgments & Contacts**

National Weather Service, Raleigh

Contact: Jeff Orrock

Warning Coordination Meteorologist

<Jeff.orrock@noaa.gov>

\(919\) 515-8209 ext. 223

North Carolina State Climate Office (NC SCO)

Contact: Dr. Ryan Boyles

North Carolina State Climatologist

<ryan_boyles@ncsu.edu>

919-515-3056

Climate Prediction Center (CPC)

National Climatic Data Center (NCDC)