Winter 2005-2006 Revisited 

Winter unofficially began a few days before Thanksgiving as a low pressure system tracked across the Mid Atlantic region and off the New England coast. This system allowed cold air to filter into the area prior to the arrival of a fast moving clipper coming out of Canada. In weather terminology, a clipper is a fast moving low pressure system that moves southeast out of Canadian (mostly from the Canadian Province of Alberta in southwestern Canada) through the Plains, Midwest, and Great Lakes region usually during the winter. This low pressure area is usually accompanied by light snow, strong winds, and colder temperatures. Another variation of the same system is called a "Saskatchewan Screamer".  Most of the precipitation associated with a clipper is along and just north of the track of the low pressure area.  So, the best clipper track to bring snow to northwest North Carolina, southwest Virginia and southern West Virginia is across the mountains of North Carolina. The Thanksgiving eve clipper tracked across the southern Appalachian Mountain and brought anywhere from a trace to one inch of snow east of the Blue Ridge and 1 to 4 inches of snow to the west (Fig 2).  Some higher elevations (above 4000 feet) saw upwards of 7 inches of snow and strong winds from this disturbance. Despite the quick decline in temperatures in the latter half of November, average monthly temperatures were 2-3 degrees above normal. Monthly precipitation amounts were also above normal even though the first 15 days were dry.

Topopgraphical Map of WFO Blacksburg County Warning Area

Figure 1.  WFO Blacksburg County Warning area geographical break down.

Snowfall Map for Nov 23, 2005

Figure 2.  Nov. 23, 2005 Clipper (Snowfall).

(Click to enlarge)

Three more winter storms developed and tracked along the Gulf Coast States and into the Mid Atlantic region in early December. These complex Gulf winter storm systems are always a difficult forecast for this area because they are coming from a warm moist climate (Gulf of Mexico), and tracking northeast into colder air (New England). As these systems move into the colder air, rain transitions into wintry precipitation (snow, sleet, and freezing rain), and this transition zone is often somewhere across North Carolina or Virginia. The track of these systems along the coast is also a critical factor affecting precipitation type and accumulations. A track off the coast and south of the area will likely produce snow for the mountains and a wintry mix of sleet and snow east of the Blue Ridge (Fig. 3-4). A westerly track (through the Tennessee and Ohio Valleys) usually results in mostly a rain event for the piedmont and a wintry mixture of sleet and snow across the mountains (Fig. 5-6). An inland track, south of the area, will often result in a wintry mix of rain, freezing rain, sleet and snow along and west of the Blue Ridge (Fig. 7-9). The east, especially the piedmont, could see rain, freezing rain, and sleet across the piedmont with an inland southern track. A wobble of the low pressure center in any scenario of 25 to 50 miles in either direction could drastically change precipitation type and accumulations.

ec. 05, 2005 Map Analysis      December 5th, 2005 Snowfall

Figure 3. Dec. 05, 2005 Map Analysis.           Figure 4. Dec. 05, 2005 (Snowfall).

(Click to enlarge each map)

December 9th, 2005 Map Analysis    December 8th and 9th, 2005 Ice Map

Figure 5. Dec. 09, 2005 Map Analysis.           Figure 6. Dec. 8-9, 2005 (Ice accretion).

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December 15th, 2005 Map Analysis    December 15th, 2005 Snowfall

Figure 7. Dec. 15, 2005 Map Analysis.           Figure 8. Dec. 15, 2005 (Snowfall).

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December 15th, 2005 Ice Accretion Map

Figure 9. Dec. 15, 2005 (Ice accretion).

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The three disturbances that plagued our area in early December (Fig. 3, 5, 7: surface analyses and Fig. 4, 6, 8-9): Snow/ice accumulations) are displayed above. The December 5th storm brought mostly snow to the area. The two following storms (December 8-9th and 15th) had more ice with them. It was this ice that accumulated into a hard shell that took several weeks to melt even as temperatures went above freezing. Some melting took place during the day but then refroze overnight when temperatures fell below freezing.

As the temperature graphs show (Fig. 15-19), early December’s cold spell kept monthly temperatures 2 to 3 degrees below normal. Once winter official started (December 22), temperatures began to warm above normal, a trend that continued into January. A total of 8 cold fronts tracked through the area during December. However, precipitation for the month was generally below normal with the exception of Southside Virginia (DAN). A majority of these 8 cold fronts brought a quick shot of cold air, (about a day), then temperatures would briefly warm back up before the next frontal passage.

As we journeyed into the New Year and deeper into winter, the colder temperatures did not follow. As a matter of fact, Blacksburg set a record for the warmest January with an average monthly temperature of 39.8 F. This broke the old record of 39.2 set in 1953. Bluefield Airport in West Virginia also had a warm January with an average monthly temperature of 42.5. This ranks second behind the record of 43.4 set in 1974. Very warm temperatures encompassed the entire area as temperatures were generally 7 to 10 degrees (F) above normal. 

There was a wide variation in precipitation amounts across the area in January. If it was not for a few good thunderstorms from a strong cold front in mid January, the area would generally be below normal (0.50 to 2.00 inches) for precipitation. When we did get precipitation to fall, the abnormally warm temperatures kept most of it as rain. A trace of snowfall was reported at Roanoke and Blacksburg during January. No snowfall was reported at Lynchburg and Danville in the month. Only a few places saw snow accumulate on the ground and that was primarily on western slopes of Southeast West Virginia (Fig. 10). As seen in the snowfall table below (Table 1), the area’s snowfall totals were 3 to 7.4 inches below normal for January.

January 25th and 26th, 2006 Snowfall Map

Figure 10. Jan. 25-26, 2006 (Upslope Snowfall).

(Click to enlarge)

Seasonal Snowfall Table

Table 1. Seasonal Snowfall (2005-06) from November 1, 2005 through March 31, 2006.

Snowfall totals rebounded towards normal in February as a few strong cold fronts moved across the region. One such front, in early February, brought severe weather to the area with an F1 tornado that touched down in Pittsylvania County. For more information about this tornado and other severe weather this winter, visit the severe weather section of this issue of NOAA ‘bout the Weather. Another strong cold front moved across the area in mid February. This winter storm (Feb. 11-12) brought the heaviest accumulating snow to the area for the winter and helped our seasonal snowfall total return to near normal. Snow accumulations from the storm over the weekend of February 11th and 12th (map) ranged from 2 to 5 inches east of the Blue Ridge and from 4 to 8 inches along and west of the Blue Ridge (Fig. 11) .  

February 12th and 13th Snowfall Map

Figure 11. Feb. 12-13, 2006 (Snowfall).

(Click to enlarge)

A few other fronts and southern stream impulses (Fig. 12-14) brought light amounts of snow to the mountains in the latter half of the month (Feb. 18, Feb. 20 and Feb. 20).  Even though the annual snowfall totals rebounded to near normal across the area, the total liquid equivalent precipitation, (rain, snow, sleet and freezing rain), for the month of February ranged from 1 to 2 inches below normal. Temperatures for February were about a degree above normal.

February 18th, 2006 Snowfall Map  February 20th, 2006 Snowfall Map

Figure 12. Feb. 18, 2006 (Snowfall).             Figure 13. Feb. 20, 2006 (Snowfall).

(Click to enlarge each map)

February 22nd, 2006 Snowfall Map

Figure 14. Feb.22, 2006 (Snowfall).

(Click to enlarge map)

The dry conditions continued into March. A few weak fronts moved across the region for the first three weeks of March with most of the rain falling across Southeast West Virginia. As this rain tried to move to the east coast, westerly downslope winds evaporated most of it. March is most noted for being a windy month and this March was no exception. However, if you combine the wind with dry conditions, enhanced fire danger arises. From January 1st to March 21st, 739 brush fires had been reported by the Virginia Department of Forestry. These brush fires damaged a total of 5133 acres. 242 of the brush fires, burning 2610 acres, occurred during the week of March 13-20, 2006. Conditions were so dry during that week that several counties across Blacksburg’s County Warning area were under a “burn ban” where no outdoor burning was permitted. Virginia averages 1449 fires burning 8338 acres per year. Some relief to the dry conditions came to the area on the first day of spring (March 20), with 1 to 3 inches of snow to mainly the Mountain Empire of Southwest Virginia and the Highlands of Northwest North Carolina. An upper level disturbance (24-25 March) also brought some much needed moisture to the area. Most of the area saw a cold rain or white rain (snow melting when hitting the ground) as the freezing level was around 3000 feet. Higher elevations, such as Hot Springs in Bath County VA and Peaks of Otter along the Blue Ridge in Bedford County, reported several inches (8.0 inches) of snow. The liquid equivalent of this snow was light (less than a 0.50 of an inch) and did little to help the dry conditions. The monthly precipitation amounts were 2 to 4 inches below normal across the area while the deficit for the year was an alarming 3 to 7 inches below normal.  In fact, the month of March was so dry for the area that records were set at 3 of the 5 climate sites that we monitor. 

The Roanoke, Danville, and Blacksburg airports all broke their old records for the driest March. Roanoke’s total monthly precipitation was just 0.35 inches, Danville’s was 0.56 inches, and Blacksburg’s was 0.69 inches. The month of March was also among the driest on record at the other two climate sites, with Lynchburg’s total of 0.76 inches being the 3rd driest, and Bluefield’s 1.71 inches being the 4th driest. The deficits for the first three months of the year are also among some of the driest on record. Danville’s total of 4.36 inches through March is their driest on record. Blacksburg’s total of 5.31 inches is their 4th driest January through March period, Roanoke’s total of 5.47 inches is their 5th driest, and Bluefield’s total of 6.35 inches is their 8th driest on record. Lynchburg’s 3 month total precipitation of 5.98 inches is not ranked in their top 10 driest, but records there go back to 1893, and would include some severe drought years in the 1930s.  You can read more about our dry spell by visiting the NOAA drought information center at http://www.drought.noaa.gov/.

With dry air over the area for much of March, diurnal temperatures swings were 30 to 35 degrees on some days. This is because dry air heats up and cools off more rapidly than moist air. The first three weeks of March had monthly temperatures 3 to 5 degrees (F) above normal. Once Spring began (20 March), daily temperatures fell below normal by 15 to 20 degrees (F) for about a week. This cold period caused the average monthly temperature to only be 1 to 3 degrees (F) above normal for the entire month of March.

Blacksburg Temperature and Precipitation Graph

Fig 15. Blacksburg VA, Temperature and Precipitation Graph Nov.1, 2005-Mar. 31, 2006.

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Roanoke VA, Temperature and Precipitation Graph

Fig 16. Roanoke VA, Temperature and Precipitation Graph Nov.1, 2005-Mar. 31, 2006.

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Lynchburg VA, Temperature and Precipitation Graph

Fig 17. Lynchburg VA, Temperature and Precipitation Graph Nov.1, 2005-Mar. 31, 2006.

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Danville VA, Temperature and Precipitation Graph

Fig 18. Danville VA, Temperature and Precipitation Graph Nov.1, 2005-Mar. 31, 2006.

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Bluefield WV, Temperature and Precipitation

Fig 19. Bluefield WV, Temperature and Precipitation Graph Nov.1, 2005-Mar. 31, 2006.

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If you would like more precipitation data or find climatic sites closer to your home,

click the Cooperative Observer Network (Coop) precipitation map below.

Cooperative Observer Network

(Click to enlarge this map, then click on station to see precipitation data)

Based on preliminary data from the National Climatic Data Center in Asheville NC, the average temperature for this past winter season (Dec. 2005-Feb. 2006) for the contiguous United States was 36.3 degrees (F). This was the 5th warmest winter on record. Around our area, the average winter temperatures were only above normal by 1 degree (F) east of the Blue Ridge, but were 2 to 3 degrees (F) above normal across the mountains. These warm temperatures for our area this winter were not record breaking. Most of the states across the country were either at or below normal for winter precipitation. WFO Blacksburg’s County Warning Area was on the order of 1 to 2 inches below normal for winter liquid equivalent precipitation.

For more information about this past winter weather events across the United States, read the full NOAA article at http://www.noaanews.noaa.gov/stories2006/s2591.htm . For other NOAA articles of weather interest go to http://www.noaa.gov/ .

Spring-Summer 2006: a Look Ahead:

La Nina makes a return.

The warm winter with above normal temperatures does not necessarily translate into an above normal temperature for this spring and summer. One factor to be considered for this summer’s forecast is a phenomenon known as La Nina. La Nina is the opposite of El Nino but still has a global effect on weather. La Nina is the cooling of ocean waters in the east-central equatorial Pacific. These conditions have been persistent during the past winter and are expected to remain into late spring and maybe this summer.  To read more about global weather pattern changes from a La Nina episode and its effects on the United States’ weather and Atlantic hurricane season, go to http://www.noaanews.noaa.gov/stories2006/s2572.htm.

Below (Fig. 20-23) are probability charts for temperatures and precipitation during a typical La Nina event. These charts and others can be found at the Climate Prediction Center (CPC) which is located at Camp Springs, Maryland http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/usdivtp/writeup.shtml. To read these charts below, there are a few things to note before a forecast can be made.

Key notes:

1)      Notice the temporal scale of the charts. April through June (spring) and July through September (summer). This is a climatological season not a calendar season.

2)      Notice the spatial distribution. These are Climatic divisions. Climate divisions represent regions that are, as nearly as possible, climatically homogeneous. Climate divisions are not the same as National Weather Service forecast zones.

3)      These particular charts show the probability (%) of whether the three month average temperature and/or precipitation will be near normal, above normal or below normal. Note: some other charts at CPC may be monthly.

4)      First thing one will notice on a map is the color. The shaded color (blue/red, green/red, white) indicates if the three month average (temperature or precipitation), will be near normal, above normal or below normal.

5)      The number indicates the probability (%) that the opposite will occur.

Example: blue shaded zone with a number 10 means that the 3 month average temperature for that division will be below the 3 month normal temperature and has a 10 percent chance that the 3 month average temperature will be warmer than the 3 month normal.

6)      Normals: An average climatological value of a meteorological parameter (temperature, precipitation, humidity, etc.) for a certain area. Climate normals are usually taken from data averaged over a 30 year period, and are concerned with the distribution of data within limits of common occurrences. Depending on the event, El Nino and La Nina, normals are averaged over a 100 year period.

7)      Average: The arithmetic sum of a set of data (numbers) divided by the total count.

Generally, during a typical La Nina episode, the Mid Atlantic region’s 3 month average spring and summer temperatures are cooler than the 3 month normals for both seasons (Fig. 20-21). There is less than a 20% chance that the 3 month average temperature will be warmer than the 3 month normal during spring and less than a 10% chance during summer. Depending on the location, precipitation amounts over either of the 3 month periods can be near or above the 3 month normals for the mountains (Fig. 22-23) . The piedmont of North Carolina could see at or below the 3 month normal precipitation for spring and summer, while the piedmont of Virginia should average near normal for both seasons.

La Nina Spring Temperature Probability image  La Nina Summer Temperature Probability image

Fig 20. La Nina Spring Temperature Prob.    Fig 21. La Nina Summer Temperature Prob.

(Click to enlarge each map)

La Nina Spring Precipitation Probabilitiy image  La Nina Summer Precipitation Probability image

Fig 22. La Nina Spring Precipitation Prob.    Fig 23. La Nina Summer Precipitation Prob.

(Click to enlarge each map)

Of course, every La Nina or El Nino event does not have the same effects on the weather in our region. Take, for example, the precipitation type problems we have here in the Mid Atlantic region when a low pressure system wobbles in a different direction by a few miles. Now imagine that scenario on a global scale. Similar to the La Nina Probability chart above, the charts below (Fig. 24-27) use global observations and complex climatic models to make a 3 month prediction. One can even get 3 month forecast a year in advance by going to CPC’s web site (http://www.cpc.ncep.noaa.gov/products/forecasts/). One thing about the charts below that was not in the previous charts was “Equal Chances” (EC). For lack of a better description, “Equal Chances” means that there is no significant signal to indicate if the 3 month average temperature will be near, above or below normal. Looking at the Temperature Outlook (April-June) below (Fig. 26) and the La Nina Temperature Probability (April-June) above (Fig. 20), some temperature probabilities do line up, especially in the southwestern United States. However, there seems to be conflicting temperature outlooks across the Southeastern United States between a normal La Nina and the official temperature outlook from the Climate Prediction Center. This is one of several reasons why the forecasters at the Climate Prediction Center have placed “Equal Chances” over the Mid Atlantic and Northeast regions for the Spring temperature outlook. Unlike the Spring temperature outlook, the Spring precipitation outlook from a normal La Nina and CPC’s Spring Precipitation Outlook are showing a correlation with a dry forecast for parts of the Mid Atlantic region. For more details on this year’s spring outlook, visit http://www.noaanews.noaa.gov/stories2006/s2595.htm.

Spring Outlook

Spring 2006 Temperature Outlook Spring 2006 Precipitation Outlook

Fig 24. Spring 2006 Temperature Outlook    Fig 25. Spring 2006 Precipitation Outlook

(Click to enlarge each map)

Summer Outlook

Summer Temperature Outlook   Summer Precipitation Outlook

Fig 26. Summer 06 Temperature Outlook.   Fig 27. Summer 06 Precipitation Outlook.

(Click to enlarge each map)

Frost-Freeze Program:

The Southern Appalachian’s trees and plants are beginning to bloom. Based on climatology, there is still the possibility that cold air could filter into the region bringing a late season frost or freeze. Those with agricultural interests will need to monitor the weather and be prepared to take protective measures if a frost or freeze does happen. The map below displays the average last frost for the area. If a frost or freeze is expected in the area after these dates, a frost advisory or freeze watch/warning will be issued by the National Weather Service.

Dates of Average Last Freeze

Average last day of freezing temperatures.

(Click to enlarge)

The NWS Blacksburg staff would like to thank our loyal and faithful trained weather spotters, HAM radio personnel, Department of Transportation (WVDOT, VDOT, and  NCDOT), County Emergency Managers and county 911 centers for their winter weather reports. Snowfall and Ice Accretion maps in this article were generated from these reports.

This climate article was written by:

Robert Stonefield

Jan Jackson

Other contributor to this article deserving recognition:

David Lawrence