**April 2007 NC Weather Review**

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**Overview**

April 2007 brought damaging freezes, strong winds, and few showers.

April 2007 will be most remembered for the hard freezes that affected
inland areas of North Carolina during the second week of the month. This
was followed by a strong wind event on April 16. The combination of hard
freezes and strong winds brought significant damage throughout the
state, especially to the agricultural community. The coldest
temperatures recorded by official National Weather Service Observations
sites during the cold spell are plotted in figure 1. The strongest winds
recorded this month were associated with the extreme gradient wind event
of April 16. The peak winds recorded on this day are depicted in figure
2.

A case event summary for this event can be found at:

<http://www4.ncsu.edu/~nwsfo/storage/cases/20070416/>

![](media/image1.png){width="7.0625in" height="3.375in"}

**Figure 1. The coldest temperatures recorded during the hard freezes of
April 6-10, 2007, recorded by official National Weather Service
observation equipment or cooperative observers.**

![](media/image2.png){width="6.989583333333333in"
height="3.1979166666666665in"}

**Figure 2. The peak wind gusts associated with the April 16, 2007 High
Wind Event, recorded by official National Weather Service observation
equipment or cooperative observers.**

There were large week to week temperature swings during April, which
were often accompanied by windy conditions. The largest swings in
temperatures came during the first two weeks of the month, when
temperatures soared into the 80s April 2-4, followed by hard freezes
April 6-10. Another week of cool weather followed the freezes during the
April 16-21 period. Then temperatures again soared to near record levels
during the last week of the month. The overall average temperatures for
the entire 30 days averaged within a degree of the 30 year normal;
however, there were very few days this month in which the daily
temperatures were considered "normal". The April 2007 average
temperatures for selected stations across the state are depicted in
figure 3.

![](media/image3.png){width="7.0625in" height="3.21875in"}

**Figure 3. Average monthly temperatures during April 2007 across North
Carolina.**

There were not many showers or rainy days during the month to help the
early spring plants and vegetation recover from the harsh freezes and
strong winds. The only significant rain events occurred April 11-12, and
April 14-15. It was during these two events that approximately 90 to 95
percent of the month's total rainfall occurred. Most reporting stations
across central sections of the state recorded near or slightly above
normal monthly rainfall totals. These areas were surrounded by very dry
conditions over the western and eastern thirds of the state, where
generally 1 to 2 inch rainfall deficits were observed. These totals
equated to only 25 to 50 percent of normal. The April 2007 monthly
precipitation totals for selected stations across the state are plotted
in figure 4.

![](media/image4.png){width="7.083333333333333in" height="3.78125in"}

**Figure 4. Estimated rainfall for April 2007. Plotted data was recorded
by National Weather Service observation systems or cooperative
observers.**

**Details**

**April 2007 Temperatures**

The up and down temperatures typically expected in the spring season
were greatly exaggerated during April. An amplified upper level flow
pattern across the United States during the first two weeks of the month
allowed for strong ridges and deep troughs. A strong ridge over North
Carolina during the first week of the month sent daily highs into the
80s at Charlotte, Greensboro, Raleigh, and Fayetteville. This period was
followed by a very deep and cold trough during the second week of April.
The temperatures under this cold trough fell at least into the 20s over
most inland sites, and as low as 1 to 20 degrees in the Mountains. This
was a 60 degree drop in temperatures from the first week of April. The
amplitude of the ridge and trough patterns weakened some during the last
two weeks of April, which resulted in less intense cold and warm
patterns.

Several periods of warm weather prior to the hard freezes of April 6-10
enhanced the damage the freezes would ultimately bring. The early warm
spell prompted many peach and apple orchards, strawberry fields, and
grape vineyards into early bud or full bloom. Then the coldest weather
of the spring hit as temperatures fell into the teens and 20s over
inland areas. These freezes occurred during 3 to 4 consecutive nights,
and wiped out a great percentage of these crops. The agricultural
communities across the Sandhills, Piedmont, Coastal Plain, and Mountain
valley regions were hardest hit, with many counties declared federal
disaster counties.

The final monthly temperatures across the state averaged very near the
30 year normal for April. Greensboro ended April with an average monthly
temperature of 58.4 degrees, which was only 0.8 degrees above normal.
Raleigh-Durham recorded an average of 60.0 degrees, 0.9 degrees above
normal. All other major reporting stations, which include Asheville,
Charlotte, Wilmington, Elizabeth City, and Cape Hatteras, recorded
monthly average temperatures slightly below normal.

![](media/image5.wmf){width="5.375in" height="3.1979166666666665in"}

**Figure 5. Daily maximum and minimum temperatures observed during April
2007 at Raleigh-Durham (RDU).**

![](media/image6.wmf){width="5.333333333333333in"
height="3.1979166666666665in"}

**Figure 6. Daily maximum and minimum temperatures observed during April
2007 at Greensboro (GSO).**

Figures 5 and 6 above, depict the daily maximum and minimum temperatures
observed at Raleigh-Durham (RDU) and Greensboro (GSO) during April 2007.
The dashed lines represent the normal maximum temperature (red) and the
normal minimum temperature (blue).

**April 2007 Precipitation**

Along with the freeze, strong winds, and extreme temperatures, there
were extended periods during April in which little or no rain fell.
Significant rain fell across the state only on April 11-12 and again on
April 14-15. All the other rain events were light and scattered
throughout the state. As it turned out, approximately 90 to 95 percent
of the monthly rainfall totals for both Raleigh and Greensboro fell in
these two rain events. The rain seemed to "cut off" on April 15, after
which there were only 1 to 2 days with very light rainfall recorded.

Most areas throughout the center of the state generally totaled 90 to
110 percent of the 30 year normal rainfall. That was not the case to the
west and to the east, where many mountain and coastal sites recorded
less than 60 percent of normal rainfall. The monthly totals generally
ranged between 4 and 5 inches across the central portions of the state,
with lesser amounts between 1 and 3 inches over the mountains and along
the coast. The highest totals occurred in the Piedmont, where over 5
inches was recorded in the city of Greensboro. The minimum rainfall
amounts occurred near and along the coast, where Beaufort in Carteret
County, only received 0.68 inches. Figure 7 is a comparison of observed
and normal precipitation for April 2007 at selected locations across
North Carolina.

![](media/image7.wmf){width="5.583333333333333in"
height="3.8020833333333335in"}

**Figure 7. Comparison of observed precipitation and normal
precipitation for March 2007 at selected locations across North
Carolina.**

**Current, Semi-Annual and Annual Temperature Trends**

The warmer than normal April at both Greensboro and Raleigh continued
the trend of above normal temperatures from March. It marked the fifth
time in six months with above normal temperatures at both Raleigh and
Greensboro. The past two winter seasons, consisting of the months of
December, January, and February, have averaged well above normal. The
warmth peaked each winter season in January, when the monthly average
temperatures averaged 6 to 8 degrees above normal.

Figure 8 illustrates the monthly temperature departures from normal at
Raleigh-Durham and Greensboro. Note that 5 of the past 6 months have
been above normal. Also of note is that nine of the past twelve months
have been warmer than normal at Raleigh-Durham. Ten of the past twelve
months have been warmer than normal at Greensboro.

![](media/image8.wmf){width="5.59375in" height="3.59375in"}

**Figure 8. Monthly temperature departures from normal at Raleigh-Durham
and Greensboro from April 2006 through April 2007.**

**Current, Semi-Annual, and Annual Precipitation Trends**

The above normal rainfall recorded at Raleigh-Durham in April broke the
string of 4 consecutive months of below normal rainfall. The rainfall
deficit during the first five months of the year lowered to 2.06 inches.
This was the fifth month in the last nine in which rainfall averaged
below normal at Raleigh. RDU finished 2006 with a 12 month surplus of
10.64 inches. Figure 9 depicts the precipitation trends at RDU during
the past year. The dry pattern during the first half of 2006 was
replaced by wet conditions from June through November 2006.

Greensboro's string of consecutive months of sub par rainfall was broken
in April. Only four of the past nine months have brought above average
rainfall. Greensboro had a rainfall deficit in 2007 of 3.00 inches
ending April 30. Greensboro completed a dramatic turn from a 7.50 inch
rainfall deficit for 2006 at the start of June, to an 8.55 inch 2006
rainfall surplus by November 30. Greensboro ended 2006 with a final
surplus of 7.22 inches. Figure 10 depicts the monthly precipitation
totals and the departure from normal during the past year at Greensboro.

![](media/image9.wmf){width="5.416666666666667in" height="3.3125in"}

**Figure 9. Semi-annual and annual precipitation trends at
Raleigh-Durham (RDU).**

![](media/image10.wmf){width="5.447916666666667in"
height="3.3645833333333335in"}

**Figure 10. Semi-annual and annual precipitation trends at Greensboro
(GSO).**

**North Carolina Water Resources Information and Outlook**

Even though some of the central Piedmont received above normal rainfall
in April, the rest of the state did not fair as well. March and April
together brought only 25 to 50 percent of the normal rainfall to the
Coastal Area, and over the Mountains. Dating back to the first of the
year, the dry weather has been especially persistent over the southwest
Mountains of North Carolina, where many areas have large rainfall
deficits of 10 to 15 inches. The more rapid than expected demise of the
El Nino conditions in the equatorial Pacific during the mid to late
winter season, seemed at least partly responsible for the dry weather.
The precipitation was well less than forecast during the winter season
from the Gulf Coast states northeastward across western North Carolina.

The drought became centered over Alabama, Georgia, Florida, South
Carolina, southern Tennessee, and far western North Carolina as of the
beginning of spring 2007. It has expanded in all directions since the
end of March, reaching across South Carolina and into western North
Carolina as of May 1, 2007. Moderate to severe drought conditions were
observed as far east as Asheville, North Carolina.

![](media/image11.png){width="5.927083333333333in"
height="4.4215277777777775in"}

**Figure 11. U.S. Drought Monitor as observed on May 8, 2007.**

Over the central and northern Piedmont of the state, the two significant
rainfall events during the middle of April kept abnormally dry
conditions at bay. These rains also kept the levels of streams, rivers,
lakes, and reservoirs at near normal. Most reservoirs that supply water
to the major cities in the center of the state were near normal on May
1, 2007. The latest Drought Monitor can be viewed in figure 11. For the
latest information concerning the drought, visit:

<http://www.ncwater.org/drought/>

**Climate Outlook for the spring and summer 2007**

The Climate Prediction Center recently released the spring and summer
outlooks. Details concerning this forecast can be found at the web
address below:

[http://www.cpc.ncep.noaa.gov/products/predictions/](http://www.cpc.ncep.noaa.gov/products/predictions/multi_season/13_seasonal_outlooks/color/page2.gif)

The headline for the spring and summer seasons has been centered on the
development of La Nina conditions in the equatorial Pacific. The rapid
demise of the El Nino during the late winter was thought to be at least
partly responsible for the very dry weather currently being observed
across the Gulf Coast states, the Tennessee Valley, and the southeastern
United States. However, forcing from the Tropical Pacific does not
typically have a great impact on the climate across the United States
during May (greatest impact occurs during the winter season). Therefore,
the developing La Nina conditions in the coming months are expected to
have little effect on the climate outlook for North Carolina during the
upcoming warm season. However, the very dry soils observed over much of
the southeastern and southern United States, including western North
Carolina at the end of April, may tilt the odds toward having a dry May.

The very dry weather observed over the southeastern United States this
winter and spring is expected to slowly improve in June and July, which
is depicted in the latest U.S. Seasonal Drought Outlook released on
April 19, 2007. This outlook is depicted in figure 12 and is valid
through August 2007.

![](media/image12.png){width="5.427083333333333in" height="4.19375in"}

**Figure 12. U.S. Seasonal Drought Outlook issued on April 19, 2007,
valid through July 2007.**

North Carolina may once again be on the northern periphery of the driest
conditions through May, but there were no clear signals concerning the
precipitation forecast for the upcoming summer season. Therefore, equal
chances of above normal, near normal, or below normal precipitation are
forecast from May through July.

The temperature forecast for the spring through summer seasons indicated
that there is an equal chance of above normal, near normal, or below
normal temperatures during the next three months as well. As is
typically the case during the spring season across North Carolina, there
will likely be large variability in temperatures and rainfall from week
to week. Some weeks will likely average above normal, while others will
be below normal. The temperature and precipitation outlooks for the
United States for the summer can be viewed in figures 13 and 14.

You can keep up with latest monthly and seasonal forecasts by visiting
the Climate Prediction Center website at
<http://www.cpc.ncep.noaa.gov/>.

Enhanced local three month temperature outlooks are now available at
<http://www.weather.gov/climate/calendar_outlook.php?wfo=rah>

![](media/image13.png){width="5.804861111111111in"
height="5.3909722222222225in"}

**Figure 13. Temperature Outlook from the Climate Prediction Center for
May through July 2007.**

![](media/image14.png){width="4.55625in" height="4.219444444444444in"}

**Figure 13. Precipitation Outlook from the Climate Prediction Center
for May through July 2007.**

**NC Weather Review Team**

Phillip Badgett

Michael Strickler