**[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
7, 2007**

Well timed rains of late October brought 2 to 5 inches of rain to all of
Central North Carolina. Many local rivers and reservoirs experienced
significant rises in water levels. However, the benefits from this one
rain event will not be enough to last through the winter. By the first
full week of November the Upper Neuse and Tar River levels were back
down to the low flows observed before the recent rain. In fact,
statewide stream flows dropped significantly the first week of November.
As of November 4^th,^ 62 percent of the stream gages in the state were
recording flows at or below the 25^th^ percentile. About 36 percent of
the stream gages recorded new record low flows for the last several
calendar days and were below the 10^th^ percentile (Figure 1).

![](media/image1.png){width="3.795138888888889in"
height="2.3381944444444445in"}

Figure 1. Stream flow at long-term stream flow gaging stations. Graphs
courtesy of the USGS.

Following the heavy rain in October, Falls Lake rose less than one foot,
while Jordan Lake and Kerr Scott reservoirs rose 2 to 3 feet (Figure 2).
Recent water level rises on the lakes do not compensate for months of
dry weather and long term water shortages. Current water inflows into
local reservoirs have decreased over the last several days falling to
below normal levels.

![](media/image2.png){width="2.6180555555555554in"
height="1.7472222222222222in"}

![](media/image3.png){width="2.6145833333333335in"
height="1.4784722222222222in"}![](media/image4.png){width="2.6381944444444443in"
height="1.479861111111111in"}

Figure 2. Lake Levels for Falls Lake and Jordan Lake from April through
October. Graphs courtesy of the USGS.

The reason for the current drought stems back to the summer of 2007
which will go down as the hottest summer on record across central North
Carolina. The record heat exacerbated the moderate drought conditions
which pre-existed earlier in the spring. By mid October, nearly 90
percent of the state was experiencing extreme to exceptional drought
conditions (Figure 3).

![](media/image5.jpeg){width="4.2in" height="3.359722222222222in"}

Figure 3. North Carolina Drought Monitor

<http://www.ncdrought.org/>

Since July, precipitation has averaged less than 50 percent of normal
over much of North Carolina as rainfall associated with tropical systems
has been minimal. During this same period, record heat was observed.
August broke the record as the hottest month and second driest August
ever, at the Raleigh Durham International Airport (RDU) (records date
back to 1944). September was the second warmest September on record,
with October following suit and ending as the warmest October on record.
Furthermore, the RDU airport recorded 83 days with temperatures 90
degrees and hotter (Figure 3). In a typical year, there are normally
only 41 days where high temperatures reach or exceed 90 degrees. All in
all, the summer of 2007 was the hottest on record at RDU.

![](media/image6.png){width="5.7965277777777775in"
height="2.796527777777778in"}

Figure 3. 2007 Maximum and Minimum Temperatures recorded at RDU.

The Piedmont Triad Airport (GSO) experienced similar heat as RDU with
August 2007 being the warmest month and the fourth driest August ever at
GSO (records date back to 1928). September 2007 made its mark as the
second warmest September on record, and October was the warmest October
on record. The Greensboro area experienced 63 days with temperatures 90
degrees or higher compared to the typical 37 days (Figure 4). Overall,
this past summer tied the second hottest summer of record at GSO and was
the second driest.

![](media/image7.png){width="5.815277777777778in"
height="2.810416666666667in"}

Figure 4. 2007 Maximum and Minimum Temperatures recorded at GSO.

Other locations The Charlotte area experienced the second driest summer
on record (records dating back to 1948). The combination of extreme heat
and dry conditions during the growing season and heavy water usage
months of July through September, resulted in significant impacts to
agriculture and water availability for numerous cities and towns in the
state.

Lake and River impacts...

Despite recent rain, river and stream levels are currently running less
than 25 percent of normal at 62 percent of the gaging sites across North
Carolina. Low water flows (less than 10 percent of normal flow) are
being recorded in headwaters of the Cape Fear, Tar, and Neuse River
basins. In addition, water inflows into Falls Lake have dropped back
down to negative values. The monthly inflows at Falls Lake ranked in the
top 10 lowest for each month from April through mid October. Negative
inflows mean the amount of water flowing into the reservoir remained
lower than the water loss from both consumption and evaporation. This
has been the story for many lakes and reservoirs across the state over
the last few months.

Falls Lake, of particular concern to the city of Raleigh, remains down
to 243 feet, more than 8 feet below normal pool, and only 36 percent the
lake's water supply pool remains. It's important to note that Falls Lake
does not go dry when the water supply pool has been depleted (236 feet);
the lake will still be 36 feet deep, but that remaining water will be
heavily sedimented and require additional treatments (Figure 5).

![](media/image8.png){width="4.014583333333333in"
height="3.0708333333333333in"}

Figure 5. Falls Lake profile courtesy of the US Corps of Engineers.

Increased Fire Danger...

The drought conditions have increased the risk of wildfires. Fall is one
of the peak fire seasons in North Carolina and given the dry conditions
greenery on many trees and shrubs contain less water than normal. Fuel
moisture values are also running low due to the prolonged hot and dry
conditions. According to the Keetch-Byram Drought Index (KBI), designed
as a drought index for fire potential assessment, the state is ranked in
the most serious category for fire danger (Figure 6). Such values of the
KBI are often associated with severe droughts and increased wildfire
occurrence. The KBI index is a number representing the net effect of
evapotranspiration and precipitation in producing cumulative moisture
deficiency, relating to the flammability of organic material in the
ground. 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/image9.png){width="3.825in" height="2.8583333333333334in"}

Figure 6. Keetch-Byran Drought Index. Graphic courtesy of the US Forest
Service

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. In

fact data show by the end of October 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 7).

![](media/image10.png){width="7.097916666666666in"
height="4.854166666666667in"}

Figure 7. 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 needs 14 to 18 inches of rain
over the next 3 months and 25 to 30 inches over the next 6 months
(Figure 8). 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/image11.png){width="3.3645833333333335in"
height="3.213888888888889in"}![](media/image12.png){width="3.279166666666667in"
height="3.21875in"}

Figure 8. 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/>

Precipitation Outlook and La Niña...

Looking ahead to this winter, the above normal rainfall needed to end
the drought appears unlikely as the National Weather Service is
predicting at least weak and more likely, moderate La Niña conditions
this winter.

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 (Figure 9). 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 world.

La Niña conditions tend to influence wintertime atmospheric flow across
the eastern North Pacific and North America. La Niña influences 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. These combine to
bring fewer storms and less moisture to the Carolinas. (Figure 10).

![](media/image13.png){width="4.064583333333333in"
height="3.7736111111111112in"}

Figure 9. Sea surface temperature graphic provided by NOAA's Climate
Prediction Center as October 10^th^ 2007.

![](media/image14.png){width="4.836805555555555in"
height="2.6951388888888888in"}

Figure 10. 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, during La Niña, 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 northern states) 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 and an increase likelihood of
above normal precipitation in the Midwest and Pacific Northwest (Figure
11).

![](media/image15.png){width="5.16875in" height="3.3444444444444446in"}

Figure 11. Winter precipitation outlook provided by NOAA's Climate
Prediction Center

When the influence of moderate to strong La Niña impacts are combined
with precipitation trends observed over the past 15 years, precipitation
typically averages 3 inches below normal during the winter months.

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 12).

![](media/image16.png){width="3.1375in"
height="2.076388888888889in"}![](media/image17.png){width="3.120833333333333in"
height="2.147222222222222in"}

Figure 12. Data provided by the National Climatic Data Center. Graphic
created by the Raleigh National Weather Service Office

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 13).

![](media/image18.jpeg){width="5.950694444444444in"
height="4.597916666666666in"}

Figure 13. 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.

The good news is cooler fall and winter days mean less water loss to
evaporation along with decreased water demand. In fact, evaporation
decreases significantly once daytime highs fall below 70 degrees. For
this reason, any significant rain received this fall and winter will
help to recharge reservoirs to some degree. However, 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)