CLIMATE SUMMARY FROM DECEMBER 2006 THROUGH MARCH 2007

by Robert Stonefield

Note: Records and normals discussed in this article pertain to NWS Blacksburg's first order climatic sites which includes Roanoke, Lynchburg, Danville and Blacksburg, VA and Bluefield, WV. To view other station climate data that may be closer to your home, visit NWS Blacksburg's Climate web site at http://www.weather.gov/climate/xmacis.php?wfo=rnk or Southeast Regional Climate Center (SERCC) at http://www.sercc.com/climateinfo/historical/historical.html.

Our Area of Coverage
Figure 1. WFO Blacksburg County Warning area geographical break down.

WINTER OVERVIEW

One would guess that this Winter (December 2006 through February 2007) was far from normal, especially since the 3 month average temperature across the WFO Blacksburg County Warning (Fig. 1) was above normal by 2oF to 4oF (Fig. 2). However, this Winter was typical when you consider there was an El Nino in the equatorial Pacific. An El Nino is the warming of ocean waters in the east-central equatorial Pacific. Generally, during an El Nino episode, the Mid Atlantic region starts the winter off with above normal temperatures into January. Then in February and March, temperatures are generally below normal. This year followed that pattern with cold air over the region beginning the last week of January and lingered into the first week of March.

Figure 2. Departure of Average Temperature (oF) from Normal (December 2006 through February 2007)
Figure 2. Departure of Average Temperature (oF) from Normal (December 2006 through February 2007).

Precipitation for an El Nino Mid-Atlantic winter should be below normal and this winter was by around 2 inches, which equates to just 50% to 75% of normal (Fig. 3), except near 4 inches in Bluefield, West Virginia. With precipitation amounts being below normal, snowfall amounts also ran well below normal with a deficit of 10 to 15 inches, except the snowfall at Bluefield was only 5 inches below normal.

Figure 3. Percent of Normal Precipitation (December 2006 through February 2007)
Figure 3. Percent of Normal Precipitation (December 2006 through February 2007).

The equatorial Pacific is currently transitioning from an El Nino to a La Nina episode. La Nina typically brings warmer than average temperatures and near to above normal rainfall to the Mid Atlantic region. La Nina can also enhance tropical activity during the summer. To read more about this summer temperature and precipitation outlooks, see the Outlook section of this newsletter.

Graph 1: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
Graph 1: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
from November 1, 2006 to March 31, 2007 for Blacksburg (RNK), VA.

Graph 2: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
Graph 2: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
from November 1, 2006 to March 31, 2007 for Roanoke (ROA), VA.

Graph 3: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
Graph 3: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
from November 1, 2006 to March 31, 2007 for Lynchburg (LYH), VA.

Graph 4: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
Graph 4: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
from November 1, 2006 to March 31, 2007 for Danville (DAN), VA.

Graph 5: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
Graph 5: Daily Highs, Lows, Normal Highs, Normal Lows, and Precipitation amounts
from November 1, 2006 to March 31, 2007 for Bluefield (BLF), WV.

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December

December was a very warm month with average monthly temperatures running 4oF to 7oF above normal (Fig. 4). Average high temperatures were in the 50s when they should have been in the mid 40s to lower 50s. Average low temperatures were warm as well, in the upper 20s to mid 30s. Normal low temperatures for the month of December are in the 20s.

Figure 4. Departure of Average Temperature (oF) from Normal (December 2006)
Figure 4. Departure of Average Temperature (oF) from Normal (December 2006).

The warmest day of the month was the 1st, with temperatures in the east ranging in the mid to upper 70s. Across the mountains, temperatures ranged from the upper 60s to lower 70s. Looking at the temperature graphs (Graph 1-5) for the 7 days following Thanksgiving, temperatures were well above normal (15oF to 20oF). Temperatures sharply fell on the 2nd, as a cold front moved through the region. In the first full week of December, temperatures remained below normal by 3oF to 7oF, and many people thought winter was here to stay. The coldest low temperatures (9oF to 20oF) were recorded on the 8th and 9th, as a strong high pressure system (Fig. 5) was centered over the area.

Figure 5. Arctic Surge of cold air (December 8, 2006). Temperature image in F
Figure 5. Arctic Surge of cold air (December 8, 2006). Temperature image in oF.

Some of the coldest spots were on the western slopes of Southeast West Virginia, where 1-3 inches of snow on the ground helped dropped temperatures into the single digits. This high remained over the area for several days, allowing the temperatures to moderate back to and above normal for day time highs starting on the 10th. However, the nights remained chilly as clear skies and dry air allowed overnight lows to radiate below normal. By the middle of the December (15th-18th ), afternoon temperatures were running 20oF above normal with records being set at Roanoke's (73oF) and Danville's (73oF) Regional Airports on the 18th. Temperatures during the second half of the month were mainly above normal. One of the few days that the temperatures were around normal was Christmas day, when rain and low clouds kept temperatures raw and chilly.

There were two notable precipitation events during the month, not including the Christmas day rain. The first precipitation event was on the 7-8th, when 1 to 3 inches of snow fell across the mountains in southeastern West Virginia and northwest North Carolina, mainly on the western slopes. This was noteworthy only because this was the first multiple county accumulating snow event of the season. The second notable precipitation event came on the 21-22 of December (Fig. 6), where half of the month's precipitation fell (0.50 to 0.80 of an inch). Below is a radar and satellite image taken on the 22nd which show several frontal boundaries converging on the region.

Figure 6. Radar Mosaic and Visible Satellite image (December 22, 2006) of rain along the east coast.
Figure 6. Radar Mosaic and Visible Satellite image (December 22, 2006) of rain along the east coast.

Moist southeasterly flow riding up the eastern slopes of the Blue Ridge produced 0.50 to 2 inches of rain across the area. Some steeper eastern slopes saw up to 3 inches of rain during this period. This was the same storm system that earlier in the month had brought the Rockies and Southern Plains their first of three Blizzards.

Even with good soaking rains on the 21st and the 25th, precipitation amounts for the month of December were 0.75 to 1.50 inches below normal (Fig. 7). Consequently, snowfall amounts were also below normal by 3 to 4 inches.

Figure 7. Percent of Normal Precipitation (December 2006).
Figure 7. Percent of Normal Precipitation (December 2006).

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January

January, like December, was another warm month. January's average monthly temperatures were around 6oF above normal (Fig. 8). In the east, average high temperatures were generally near 50oF with Southside the warmest, in the lower 50s. Typically, average highs in the east are in the mid to upper 40s. The mountains saw average highs in the mid to upper 40s. Their normal highs are near 40oF. Overnight lows were also warm, with the average lows in the east in the lower 30s. Normal lows for this time of year are in the mid 20s. West of the Blue Ridge, average January lows ranged from 25oF to 30oF. Normal lows for the west range from 20oF to 25oF.

Figure 8. Departure of Average Temperature (oF) from Normal (January 2007)
Figure 8. Departure of Average Temperature (oF) from Normal (January 2007).

Frontal boundaries the first two thirds of the month generally stalled or slowly moved through the Ohio River valley. With these fronts being to the north and west of the area, warmer temperatures remained across the region. Some daily high temperatures were record setting (on the 4th and the 14th) and were 20oF or so degrees above normal. A couple of daily low temperatures were warmer than the normal high temperatures for their date (5th and 14th). Around the 18th, true winter began as a couple of Arctic fronts brought very cold air into the region. Temperatures in the latter third of the month only shot well above normal one day (27th). Other days, mountain sites struggled to reach afternoon normals, and some days struggled to reach freezing. The coldest temperatures recorded for the month were on the 29th. Overnight lows dropped into the teens across the east with single digits in the west.

Precipitation for the month of January was generally an inch or so below normal for most of the area (Fig. 9). The only area that saw above normal precipitation for the month was Southside, VA. Just over half of the Southside monthly precipitation fell overnight (Dec. 31-Jan. 1), when a stalled frontal boundary (Fig. 10) was draped over eastern Virginia and North Carolina.

Figure 9. Percent of Normal Precipitation (January 2007).
Figure 9. Percent of Normal Precipitation (January 2007).

Figure 10. Radar Mosaic and Visible Satellite image (January 1, 2007)
Figure 10. Radar Mosaic and Visible Satellite image (January 1, 2007)
of convective rain showers along the east coast.

As seen in Figures 11 and 12, 3 to 4 inches of rain fell across the area causing widespread flooding along the Dan River. South Boston, located along the Dan River, finally went below flood stage on January 4th.

Figure 11. NWS Blacksburg Radar (January 1, 2007) displaying line of convective showers
Figure 11. NWS Blacksburg Radar (January 1, 2007) displaying line of convective showers
moving slowly to the east. White boxes are polygon flood warnings.

Figure 12. Estimated precipitation amounts from NWS Blacksburg radar (January 1, 2007).
Figure 12. Estimated precipitation amounts from NWS Blacksburg radar (January 1, 2007).

Between the 4th and the 8th of the month, several Gulf of Mexico waves were riding along a slow moving cold front in the Ohio River Valley. With each passing wave, the front slowly moved to the south and east. During this time, temperatures across our area were well above freezing and only rain (0.80 to 2.0 inches) fell across the area. On the 9th, the cold front was to our south and a clipper system finally brought some snow to the region. Most of the snow melted shortly after hitting the warm ground, but higher elevations and western slopes of NW NC saw up to 8 inches by the time the clipper exited the east coast (Fig. 13).

Figure 13. Snow from the January 9, 2007 Clipper.
Figure 13. Snow from the January 9, 2007 Clipper.

By mid January, warm air reentered the region as another frontal boundary stalled from eastern Texas to the Ohio Valley. On the 18th, this front finally moved south of the region (Fig. 14). Temperatures dropped to near freezing (Fig. 15) and as a coastal wave tracked along the front, light freezing rain and snow fell across the area.

Figure 14. Radar Mosaic and Visible Satellite image (January 18, 2007)
Figure 14. Radar Mosaic and Visible Satellite image (January 18, 2007)

Figure 15 shows temperatures across the area January 18th, 2007 at 7 pm est
Figure 15. Temperature (oF) Image. Coastal wave tracking northeast along a
frontal boundary at 00Z 19 January 2007.

A stronger wave moved across the southeast and along the coast on the 21st. Initially, the air column over the area supported snow (Fig. 16), but as the wave tracked through the southeastern states, warm southwesterly flow brought warmer temperatures in aloft. This allowed the precipitation to change to sleet and freezing rain as low levels and surface temperatures (Fig. 17) were at or below freezing.

Figure 16. Widespread Sleet and freezing rain.
Figure 16. Widespread Sleet and freezing rain.
Radar Mosaic and Visible Satellite image (January 21, 2007).

Figure 17. Temperature (oF) Image (January 21, 2007).
Figure 17. Temperature (oF) Image (January 21, 2007).

Liquid amounts for this storm ranged from 0.30 to 1.00 inch (Fig. 18). If the air column would have remained below freezing, the area would have seen 3 to 10 inches of snow. However, the precipitation did change over to an icy mix, which limited snow and sleet accumulations to 1 to 2 inches (Fig. 19). At the end of the event, more freezing rain was accumulating than snow and sleet. Up to a quarter of an inch of ice from freezing rain was reported especially along eastern slopes of the Blue Ridge.

Figure 18. Liquid Precipitation amounts from the January 21, 2007 winter storm.
Figure 18. Liquid Precipitation amounts from the January 21, 2007 winter storm.

Figure 19. Snow/Sleet accumulations and Ice accretions from the January 21, 2007 winter storm.
Figure 19. Snow/Sleet accumulations and Ice accretions from the January 21, 2007 winter storm.

From January 21st on in to mid February, Arctic air continued to pump into the region and was being reinforced about every three days. Accompanying each arctic surge was enough moisture to produce mainly mountain snow showers (25th and 28th). The Arctic front on the 28th not only brought 6 to 8 inches of snow to western slopes (Fig. 20) of Southeastern WV, but single digit temperatures and negative wind chill values to the mountains.

Figure 20. January 28, 2007 mountain snowfall from an Arctic front.
Figure 20. January 28, 2007 mountain snowfall from an Arctic front.

Snowfall for the month was near normal for the western slopes of Southeastern WV. Areas along and east of the Blue Ridge saw very little snow and had a monthly snowfall deficit around 6 inches.

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February

As we moved into the heart of winter, daily temperatures dipped to 10oF to 20oF degrees below normal. The coldest day was on the 5th when arctic air kept afternoon high temperatures in the teens across the mountains to lower 20s in the foothills and piedmont sections of southwest Virginia. Southside Virginia was the warm spot with temperatures reaching the mid 30s on this day. Morning lows on the 6th were extremely cold under this arctic air mass with temperatures ranging from 0oF to 15oF across the area. Unfortunately, the wind was blowing with this cold air and wind chill values dropped down into the -5oF to -15oF range. Even though the temperatures moderated to near or above normal the last week of February, the average monthly temperatures ran 3oF to 6oF below normal (Fig. 21).

Figure 21. Departure of Average Temperature (oF) from Normal (February 2007)
Figure 21. Departure of Average Temperature (oF) from Normal (February 2007).

February 2007 average monthly temperature were cold enough to rank in the top 10 for the coldest February on record (Table 1). The only climatic site that did not make the top ten was Lynchburg, however their period of record started in 1893 where the other sites (Roanoke, Danville, Blacksburg, and Bluefield) period of record started in the 1940s and 1950s.

Station

February Ranking

Average Monthly Temperature February 2007

Normal February Monthly Temperature

Coldest February on Record Year Period of Record
Roanoke
9
34.2oF
39.1oF
29.3oF
1979
1948
Lynchburg
12
32.3oF
37.8oF
27.9oF
1979
1893
Danville
10
36.8oF
39.7oF
32.1oF
1978
1948
Blacksburg
8
29.7oF
33.5oF
23.5oF
1978
1952
Bluefield
8
29.5oF
36.1oF
23.3oF
1978
1959
Table 1. Average Monthly Temperature data for February.

There were several precipitation events across Blacksburg's County Warning Area during the month. The first event, which came in on the 1st, was expected to bring several inches of snow to the area. However, convection (Fig. 22) along the Southeast U.S. and Gulf of Mexico coast, cut off the flow of moisture into the area and only light amounts of snow were reported. As seen in figure 23, the snow line made it as far north as highway 460 then exited the east coast by the evening.

Figure 22. Showers and Thunderstorms across the Southeast US.
Figure 22. Showers and Thunderstorms across the Southeast US.
Radar Mosaic and Visible Satellite image (February 1, 2007).

Figure 23. NWS Blacksburg Radar (February 1, 2007) displaying light snow advancing to the north.
Figure 23. NWS Blacksburg Radar (February 1, 2007) displaying light snow advancing to the north.

Most of the Blacksburg County Warning area that missed out on the February 1st snow, had snow move in on the 6th (Fig. 24) as a clipper tracked across the region. The heaviest snow fell across the Greenbrier Valley and into the Allegheny Highlands, with reports of 5 to 8 inches (Fig. 25). The New River, Roanoke, and Southern Shenandoah Valleys, eastward through the Lynchburg area also saw a fair share of snow with 3 to 5 inches falling during the evening. Outside of these areas, only light accumulations were reported, generally an inch or less.

Figure 24. NWS Blacksburg Radar (February 6, 2007) displaying snow
Figure 24. NWS Blacksburg Radar (February 6, 2007) displaying snow advancing to
the east from a clipper moving across the Ohio Valley.

Figure 25. Snow accumulations from the February 6, 2007 Clipper.
Figure 25. Snow accumulations from the February 6, 2007 Clipper.

On February 13-14th, A complicated weather scenario set-up over the region as a low pressure system tracked through the Tennessee valley while a secondary low developed along the Carolina coast. While these two Lows were jockeying for position, cold surface air was being drawn into the are from the north east. This scenario (Fig. 26), usually brings a wintry mix of rain, freezing rain, sleet and snow into the area. The precipitation began as sleet but quickly changed over to freezing rain, which persisted through much of the day, in some areas. Ice Accretions of a quarter of an inch were common across much of southwest Virginia with significant icing greater than a half of an inch along eastern slopes of the Blue Ridge from Floyd county northeast to Amherst County (Fig. 27). Bedford and higher elevations of Bath and Allegheny counties also received greater than a half inch of icing. Once the front moved through the region, upslope snow showers reigned supreme along western slopes of Southeastern West Virginia (Fig. 28).

Figure 26. Ice storm February 13-14, 2007.
Figure 26. Ice storm February 13-14, 2007. Frontal analysis with dew points (oF) image.

Figure 27. Ice accretions from the February 13-14, 2007 storm.
Figure 27. Ice accretions from the February 13-14, 2007 storm.

Figure 28. Upslope snow showers following the February 13-14, 2007 ice storm.
Figure 28. Upslope snow showers following the February 13-14, 2007 ice storm.

The liquid precipitation amounts for the month of February were around an inch or so below normal, which equates to just 50% to 75% of normal (Fig. 29). Nearly half of the month's liquid precipitation fell during the ice storm on February 13th. Monthly snowfall amounts were also below normal along and east of the Blue Ridge (2 to 4 inches).

Figure 29. Percent of Normal Precipitation (February 2007).
Figure 29. Percent of Normal Precipitation (February 2007).

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March

Unlike February, March's average monthly temperature was well above normal by 4oF to 7oF (Fig. 30). A two sites (Roanoke and Bluefield) set new records, with March 2007 being the warmest (Table 2) on record. It was the second warmest March on record in Blacksburg, and the third warmest on record in Danville. In Lynchburg, where there is a longer period of record, it was only the 20th warmest March. Even though most of March's daily highs ran above normal, it was the 7 day stretch from the 22nd through the 28th that really pushed the average monthly temperature to record levels. During this period, temperatures were 15oF to 25oF above normal with the warmest days being the 27th and 28th. Of our 5 Climatic sites, several daily record highs were broken including 2 at Roanoke, 2 at Danville, 4 at Blacksburg and 5 at Bluefield. Overnight lows were also above normal through most of the month. As a matter of fact, Roanoke and Bluefield set 5 records and Blacksburg set 4 for warmest overnight lows. Most of these new records came during the third week warm spell. The coldest night was on the 19th when temperatures fell between 20oF and 25oF east of the Blue Ridge and into the teens across the mountains.

Figure 30. Departure of Average Temperature (F) from Normal (March 2007).
Figure 30. Departure of Average Temperature (oF) from Normal (March 2007).

Station
March Ranking

Average Monthly Temperature March 2007

Normal March Monthly Temperature

Warmest March on Record Year Period of Record
Roanoke
1
53.2oF
47.2oF
53.2oF
2007
1948
Lynchburg
20
50.3oF
46.2oF
57.1oF
1921
1893
Danville
3
52.9oF
47.9oF
53.4oF
1990
1948
Blacksburg
2
47.8oF
41.4oF
48.5oF
1976
1952
Bluefield
1
52.0oF
44.6oF
52.0oF
2007
1959
Table 2. Average Monthly Temperature data for March.

One reason why the March 2007 temperatures were above normal, was that cold frontal boundaries rarely moved south of the Ohio Valley. If a frontal boundary did move across the area, it was generally a warm front (Fig. 31).

Figure 31. Frontal analysis with temperature (F) image on March 13, 2007.
Figure 31. Frontal analysis with temperature (oF) image on March 13, 2007.

Precipitation amounts for the month varied, depending on your location (Fig. 32). Lynchburg and Bluefield were around normal. Locations that saw a deficit, half to one inch of rainfall, were Roanoke and Danville. Blacksburg was the odd site out, with a surplus of nearly 3 inches of rain for the month. The well above normal rainfall for Blacksburg was due in part to two days of record rainfall, (2.21 inches on the 16th and 2.93 inches on the 28th). Blacksburg's total rainfall in March of 6.64 inches ranked the 4th highest since 1952. The wettest March on record was 8.33 inches set in 1975.

Figure 32. Percent of Normal Precipitation (March 2007).
Figure 32. Percent of Normal Precipitation (March 2007).

There were three significant rain events during the month (1st, 16th and 28th). On the 1st, a slow moving cold front tapped into some Atlantic moisture to produce widespread moderate to heavy rain of 1 to 3 inches (Fig. 33). The highest amounts were on the eastern slopes of the Blue Ridge. This caused small stream flooding in several counties, minor river flooding along the Dan River, in South Boston, and the James River at Bremo Bluff, and moderate flooding along the Greenbrier River in Alderson.

Figure 33. 24 hour rainfall amount from March 01, 2007.
Figure 33. 24 hour rainfall amount from March 01, 2007.

The second significant rainfall event came on the 16th when a strong cold front moved to the east coast (Fig. 34). This event produced another 1 to 3 inches of rain across the area. The highest amount of rainfall for this event was again along the eastern slopes of the Blue Ridge. Sloan Branch in Botetourt County reported 3.95 inches of rain for this event. Once the front was along the east coast and cold air was entrenched over the region, western upslope snow showers fell across the mountains particularly southeast West Virginia (Fig. 35). The Quinwood and McRoss area saw up to 8 inches of snow on the 17th.

Figure 34. Frontal analysis with temperature (F) image on March 17, 2007.
Figure 34. Frontal analysis with temperature (oF) image on March 17, 2007.

Figure 35. Snow accumulations (inches) on March 17, 2007.
Figure 35. Snow accumulations (inches) on March 17, 2007.

The third significant event for the month was on the 28th, as a cold front was draped across the area (Fig 36). During the afternoon, thunderstorms began to fire along the front. Some of these storms produced frequent lightning, heavy downpours and large hail. These storms were slow moving and produced locally heavy downpours of 3 to 4 inches of rain in less than an hour (Fig 37). This caused some flash flooding on small creeks in Montgomery County and in Ashe County in the Northwest North Carolina Mountains. Some of these slow moving storms produced hail which covered the ground like snow, with the largest coverage in the Meadows of Dan area.

Figure 36. NWS Blacksburg Radar and Frontal Analysis for March 28, 2007.
Figure 36. NWS Blacksburg Radar and Frontal Analysis for March 28, 2007.

Figure 37. Estimated precipitation amounts from NWS Blacksburg radar (March 28-29, 2007).
Figure 37. Estimated precipitation amounts from NWS Blacksburg radar (March 28-29, 2007).

Snowfall amounts for March were below normal by 3 to 4 inches. The western slopes of Southeast West Virginia were the only areas to see above normal snow fall, mainly due to the upslope event on the 17th. Bluefield's monthly snowfall was above normal by 1.7 inches.

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