CLIMATE SUMMARY FOR

THE SUMMER OF 2008 (JUNE-AUGUST)

 

Temperatures
Rainfall
Severe Weather

 

Note: Records and normals discussed in this article pertain to NWS Blacksburg's first order climatic sites which include 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 the Southeast Regional Climate Center (SERCC) at http://www.sercc.com/climateinfo/historical/historical.html.

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

What a difference a year makes

Part 1: Temperatures

The Summer of 2008 (June 1-August 31) started out like last year with temperatures in early June running above normal by 10F to 15F. With the passing of a cold front during the middle of June, temperatures fell back to normal levels for the majority of the summer. There were a few week-long heat spells during this past summer but nothing like the Summer of 2007. The Summer of 2007 saw 151 days of temperatures 90F or warmer (summing the total from all 5 first order climate sites, Table 1). By comparison, the Summer of 2008 only had 101 days. The numbers of days being 90F or warmer for this summer was around normal for areas east of the Blue Ridge. Across the mountains, the number of days being 90F or warmer was below normal with Blacksburg only seeing 3 days (normal is 6) and Bluefield not seeing any (normal is 2). In 2007, Blacksburg saw 12 days of 90F or warmer while Bluefield had 14 days. Blacksburg's three 90F days came during the initial summer warm spell in early June.

 
Station
2007
2008
NORMAL
ROANOKE
42
25
24
LYNCHBURG
29
28
21
DANVILLE
54
45
43
BLACKSBURG
12
3
6
BLUEFIELD
14
0
2
Total
151
101
96
Table 1. Number of 90F days or warmer from June through August of 2007 and 2008.

 

Average summer temperatures (Figure 2) were within a degree of normal with readings at Roanoke at 75.4F, Lynchburg 74.5F, Danville 76.8F, Blacksburg 69.4F, and Bluefield 70.9F. One of the reasons why this past summer was cooler than the Summer of 2007 is that more cold fronts moved across the region. With more cold fronts comes more clouds and rain, and eventually cooler air behind the systems. Last summer, the majority of the fronts only made it as far south as the southern Ohio Valley. This kept the area in the warm sector with little rain, and warmer than normal temperatures were a result.

Departure of Average Temperature
Figure 2. Departure of Average Temperature (oF) from Normal (June 2008 through August 2008).

 

Blacksburg, VA climate Graph 2008
Graph 1. Blacksburg, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through August 2008.

Roanoke, VA climate Graph 2008
Graph 2. Roanoke, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through August 2008.

Lynchburg, VA climate Graph 2008
Graph 3. Lynchburg, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through August 2008.

  Danville, VA climate Graph 2008
Graph 4. Danville, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through August 2008.

  Bluefield, WV climate Graph 2008
Graph 5. Bluefield, WV, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through August 2008.

To see archive graphs of annual and monthly temperature and precipitation, visit our climate site at http://www.weather.gov/climate/local_data.php?wfo=rnk.

What a difference a year makes

Part 2: Rainfall

As you may recall, rainfall was well below normal in the summer of 2007, and drought conditions worsened.With the exception of Lynchburg, most sites were around normal for rainfall in the summer of 2008. (Figure 3). Table 2 displays how close to normal each of the NWS Blacksburg's first order climate stations were and how this summer compared to last summer. One station, Lynchburg, looks out of place with near normal rainfall during the summer drought of 2007 and well below normal rainfall in 2008 when tropical systems brought beneficial rain to most of the area. In 2007, Lynchburg got hit with more slow moving thunderstorms than the other sites. Whereas in 2008, strong storms and tropical rainfall mostly evaded Lynchburg. In a year where a couple of tropical systems brought beneficial rain to the area, Lynchburg's 5.74 inches of rain was its 9th driest summer on record. Lynchburg's period of record dates back to 1893.

Percent of Normal Precipitation
Figure 3. Percent of Normal Precipitation (June 2008 through August 2008).

 
Station
2007
2008
NORMAL
ROANOKE
7.34
12.96
11.42
LYNCHBURG
11.74
5.74
11.59
DANVILLE
6.76
11.98
11.48
BLACKSBURG
7.75
10.43
11.78
BLUEFIELD
7.73
11.32
11.06
Table 2. Rainfall amounts from June through August of 2007 and 2008.

 

The summer of 2008 started off either abnormally dry, or with moderate drought conditions, (Figure 4). Rainfall was scattered and unorganized through most of the summer, and drought conditions worsened, reaching their peak toward the end of August, with moderate to severe drought across most of the area, and even extreme drought in the northwest North carolina mountains and foothills, (Figure 5). The most beneficial rains came from tropical systems (remnants of FAY and Tropical Storm Hanna) late in the season. Remnants of Fay effected the area on August 27th and 28th. Rainfall amounts over these two days were generally 2 to 5 inches (Figure 6). Across the northwest North Carolina mountains, particular along east slopes, rainfall amounts were 7 to 10 inches. This heavy rainfall at the end of the summer reduced the drought conditions by a category, with most of the area in moderate drought by September 2nd, (Figure 7).

 

U.S. Drought Monitor graph issued June 3, 2008
Figure 4. U.S. Drought Monitor graph issued August 26 2008.

U.S. Drought Monitor graph issued August 26 2008
Figure 5. U.S. Drought Monitor graph issued August 26 2008.

Rainfall amounts from Fay
Figure 6. Estimated rainfall amounts from the remnants of Tropical Storm Fay (August 27-28, 2008).

U.S. Drought Monitor graph issued September 4, 2008
Figure 7. U.S. Drought Monitor graph issued September 4, 2008.

 

Tropical Storm Hanna (September 6, 2008) was another system that brought beneficial rain to parts of the area. Unlike Fay, Hanna's rain shield (Figure 8) was more compact and brought rain to mainly the piedmont sections of the Blacksburg County Warning Area. Areas east of Highway 29 saw 3 to 6 inches of rain with locally heavier amounts to near 8 inches, (Figure 9), from Hanna, while along the Blue Ridge in Virginia only averaged a half to one inch of rain.

Radar mosaic Of tropical Storm Hanna
Figure 8. NWS Radar Mosaic (September 6, 2008) of Tropical Storm Hanna tracking across North Carolina.

Rainfall amounts from Tropical Storm Hanna
Figure 9. Estimated rainfall amounts from NWS Blacksburg radar (September 6, 2008) Tropical Storm Hanna.

 

How important are hurricanes? In a matter of about 2 weeks, rainfall from two tropical systems brought Danville's annual precipitation (Figure 10) from nearly 12 inches below normal to near normal. Despite the large amount of rain these systems brought to Southside Virginia, only minor flooding was reported.

Danville, VA 2008 rainfall
Figure 10. Danville, VA 2008 precipitation amount through September 10th.

 

What a difference a year makes

Part 3: Severe Weather

The summer of 2008 had nearly 55% more reports of severe weather (525) than the summer of 2007 (289). The graph below (Graph 6) shows the difference between 2007 (blue) and 2008 (red) for each month of the summer. As you can see from the graph, most of the summer 2008 severe weather occurred in the months of June and July.

Severe Summer 2007-2008
Graph 6. Severe weather by summer months (June, July, and August) for 2007 and 2008.

There were three events during the summer of 2008 with widespread and numerous severe weather reports.

The first severe weather outbreak occurred on June 22, (78 severe weather reports). Storms initially developed around noon along the Blue Ridge Mountains in southwest Virginia and northwest North Carolina. A line of thunderstorms then pushed east into the piedmonts of southwest Virginia and northwest North Carolina, eventually producing a couple of supercells out east during the afternoon with large hail cores. More lines of severe thunderstorms moved into the mountains from the west for a second round during the evening, with a couple of rotating supercells that produced widespread large hail and wind damage. A second line worked southeast off the Blue Ridge Mountains after dark with continued damaging winds and embedded deeper cores containing hail aided by cooling aloft. This line eventually slowed upon nearing the VA/NC border resulting in a flash flood threat across the piedmont and foothills into the overnight. These flash flood warnings in combination with the severe warnings brought the total number of warnings to over 50 for the event, with warnings of some sort in place for over 12 hours!

The second widespread severe weather event occurred over a 3 day period from July 7 through July 9, (96 severe weather reports). A closed upper low drifted slowly eastward across the region Monday 7/7 and Tuesday 7/8. The low was over the southwest VA mountains Monday, and the western VA piedmont Tuesday. We had a deep moist profile Monday with a cold pool aloft promoting steep mid level lapse rates. As a result, most of the thunderstorms that developed became strong and produced large hail. On Tuesday, a slowly weakening area of showers and thunderstorms stayed over much of the mountains through early afternoon. With the cold pool over the piedmont, storms developed early and became severe with damaging winds. After heating in the afternoon, more storms developed in the mountains by 430 pm and moved east into the piedmont by early evening, producing more reports of damaging winds. On Wednesday, 7/9, the closed upper low moved east of the area, but left an upper trough over the region with more energy digging into the trough. Thunderstorms developed east of the Blue Ridge ahead of a weak secondary cold front during the mid-afternoon hours. The storms were generally fast-moving and high wind producers. There was widespread tree damage including areas around Roanoke.

The third and final widespread severe weather event occurred over two days, July 22 and 23, (76 reports of severe weather). Scattered thunderstorms developed in the northwest North Carolina piedmont on the evening of July 22. Meanwhile, a line of thunderstorms ahead of a cold front approached the area from the west. Outflow from the northwest North Carolina piedmont storms generated scattered clusters of severe thunderstorms across the northwest North Carolina and southwest Virginia piedmonts up to the Blue Ridge producing large hail and damaging winds, while the more organized line of severe thunderstorms moved into the mountains, also producing large hail and damaging winds. The activity decreased in strength by 1100 pm. The cold front which was approaching the area on the July 22 moved through the region during the evening hours of the 23rd. Although instability was rather marginal, cooling aloft allowed for a broken line of severe thunderstorms to propagate across the Blue Ridge Mountains of northwest North Carolina and southwest Virginia, into the piedmont during the late evening, producing large hail and damaging winds.

 

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This climate article was written by:

Robert Stonefield and Jan Jackson

Other contributors to this article deserving recognition:

Jim Hudgins