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.
Figure 1. WFO Blacksburg County Warning area geographical break down.
One Hot Summer
This Summer (June 1-August 31, 2007) saw some hot temperatures over the region. Roanoke's 2007 average summer temperature of 77.4oF was the warmest on record since 1948. Danville's (77.7oF) and Lynchburg's (75.1oF) summer temperatures weren't record breaking. However, Danville and Lynchburg still managed to have summer temperatures average above normal, 0.5oF and 1.1oF respectfully. Roanoke had 42 days that were equal to or greater than 90oF (27 of them were in August) and 4 days of 100oF or better. Seven of these daytime highs were new records. Roanoke also saw their warmest overnight low of all time on August 9th with a temperature of 79oF. Danville's number of days equal to or greater than 90oF was 54 (29 of them were in August) and 5 days of 100oF or better. Just like Roanoke, 7 of these daytime highs were new records. Lynchburg was warm but only saw 29 days of 90oF or warmer. Lynchburg did not see 100oF this Summer and only managed to set 2 daily high records.
The mountains also had a hot Summer with the three month average temperature being 2oF to 5oF above normal (Fig. 2). Bluefield's average summer temperature of 74.2oF, 4.9oF above normal, was the warmest on record since 1959. Blacksburg's 71.5oF was the 6th warmest on record (since 1952) and was 2.1oF above normal. Bluefield, known as the "Nature's Air Condition City", saw 14 days of 90oF or warmer temperatures. Bluefield also set 19 new high temperature records and 13 warmest low temperature records this Summer. Twice Bluefield hit 95oF (August 16th and 24th), which is the second warmest temperature ever at the airport. The warmest day was 96oF set on July 16, 1988. When Bluefield's high temperature for the day is equal to or greater than 90oF, the city hands out free lemonade to residents the next day. Nearly 900 gallons of lemonade were served this Summer. Blacksburg also saw several days of 90oF or warmer (12 times). Blacksburg set 9 new record high temperatures this summer.
Figure 2. Departure of Average Temperature (oF) from Normal (June 2007 through August 2007).
The culprit of these above average summer temperatures was a ridge of high pressure located over the Gulf states (Fig. 3). When this ridge drifted over the southeastern coastal states that is when the region saw most of the record breaking heat (August). Consequently, this ridge kept most of the area's convection scattered while deterring any strong tropical systems from entering our region. One tropical system did bring beneficial rain to the area early this Summer, before the ridge took residence over the Gulf coast. Tropical Storm Barry (June 3) brought 1 to 3 inches of rain to the area. Remnants of one other tropical system (Erin) did bring some rain to the area in mid August, but that was scattered with a few severe thunderstorms.
Figure 3. Average 2007 Summer weather pattern. 500 mb heights (m).
With most of the rain being scattered this Summer, precipitation ranged from 4 to 5 inches, or around 65% below normal (Fig. 4). Danville's 6.76 inches of rain was the driest Summer on record. Blacksburg, Bluefield, and Roanoke also had their top 10 driest summer on record, 7.55 (4th), 7.73 (6th), and 7.34 (9th) respectfully. Normal summer precipitation amounts at these locations is around 11.25 inches. Lynchburg's summer precipitation amount (11.74 inches) was near normal, with 7.19 inches in July. The lack of rain this Summer contributed to the area being placed in a moderate to severe drought (Fig. 5). Annual precipitation totals were running around 2 inches below normal near Lynchburg to 9 inches below normal at Roanoke and Danville at the end of August (Graphs 1-5). Across the mountains, Bluefield's annual deficit was 7 inches and Blacksburg's was just under 9 inches.
Figure 4. Percent of Normal Precipitation (June 2007 through August 2007).
Figure 5. U.S. Drought Monitor graph issued August 28 2007.
Graph 1. Blacksburg, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through September 2007.
Graph 2. Roanoke, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through September 2007.
Graph 3. Lynchburg, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through September 2007.
Graph 4. Danville, VA, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through September 2007.
Graph 5. Bluefield, WV, Daily Max/Min Temperatures (oF) and yearly precipitation amounts (inches) through September 2007.
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.
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The unofficial start to Summer began May 26th (similar to last year), as mean daily temperatures went 5oF to 10oF above normal across the area. These warm temperatures were a result of a strong area of high pressure over the southeastern United States (Fig. 6), abundant sunshine, and dry conditions. Depending on how strong these highs are and how long they stay in a region, very warm to hot conditions could persist for weeks/months with temperature records possible. With more of the ridge over the western half of Blacksburg's CWA, Bluefield, WV had their 5th warmest May since 1959. Contributing to this top 5 ranking at Bluefield were 6 record daily highs and 4 new records for the warmest low temperature. Blacksburg also set a few records on daily highs during the month. Despite the above normal warming trend at the end of the month, the warmest day was actually on the 1st of the month (mid 80s to lower 90s). These temperatures were 15oF above normal for this time of year. A few days later, temperatures fell below normal for about a week as a wedge of cooler air worked south down the east coast. For May 2007, the average monthly temperature was 3oF to 4oF above normal along and west of the Blue Ridge (Fig. 7). In the east, where the cool wedge kept temperatures down longer and the southeastern ridge had less of an effect, monthly average temperatures were around normal.
Figure 6. Evening surface analysis on May 27, 2007
Figure 7. Departure of Average Temperature (oF) from Normal (May 2007).
May is normally one of the area's wettest month of the year for Blacksburg’s County Warning Area (CWA), based on the 30 year normals from 1971 to 2000 of over 80 Cooperative Observing locations. The mean monthly precipitation for the area this May, based on the same Cooperative Observing locations, was only 1.98 inches. Normal precipitation for May is 4.42 inches across the area. By comparison, last year's monthly precipitation was 2.14 inches. This average may have been lower this month if it were not for a few new records for daily rainfall. One record daily rainfall was recorded at Roanoke on the 26th (1.34 inches). The previous record was 0.45 inches in 1948. On the 3rd, Bluefield had 1.48 inches of rain (old record was 0.53 inches in 1983). Despite this daily record, Bluefield still had one of their driest May (ranked 8th) on record since 1959 (2.79 inches). Danville recorded its second driest May since 1948 with 1.38 inches of rain. The driest was in 1999 with 1.13 inches. These below normal monthly amounts (Fig. 8) brought the yearly precipitation deficits to 2 to 5 inches in the east and 1 to 4 inches in the west.
Figure 8. Percent of Normal Precipitation (May 2007).
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June followed in the footsteps of May with above normal average monthly temperatures. June's average monthly temperature departure (Fig. 9) was 1.5oF to 3.5oF above normal along and west of the Blue Ridge. East of the Blue Ridge, monthly average temperatures ran around a degree above normal. Toward the Alleghany Highlands, temperatures were about normal.
Figure 9. Departure of Average Temperature (oF) from Normal (June 2007).
Just like May, after the first couple of days of the month being above normal, temperatures fell to around normal for about a week for the entire area. These near normal temperatures were aided by Tropical Storm Barry bringing rain to the region while it tracked along the east coast. Cooler drier air came in Barry's wake until the 7th when the ridge of high pressure reestablished itself over the southeastern coast states. Temperatures over the next week trended warmer. On June 14th and 15th, daily high temperatures struggled to warm and remained in the 60s. This cool down was in part due to a back door cold front (Fig. 10) that came south along the east coast. Once the clouds and rain exited the area, temperatures rebounded above normal for the rest of the month as high pressure was once again over the southeastern coast states. Flow around this ridge brought in warm moist air to the region. Daily high temperatures were running about 5oF above normal with dew points in the 60s during this period. The only time daily temperatures fell below normal was if an isolated shower crossed over the area. These showers were few and far between.
Figure 10. Evening surface analysis on June 4, 2007
With limited rain across the area for the majority of the month, temperature records were in jeopardy. Bluefield's average monthly temperature of 71.5oF tied the warmest June on record (1984). Bluefield also set 8 new daily high records during the month. Roanoke, Danville, and Blacksburg each had one new record high. On the other hand, Danville and Lynchburg had a couple of record lowest highs for the month. These cooler temperature kept eastern average monthly temperature near normal while other sites were above normal for the month. The warmest day of the month for the area was the 18th when temperatures topped out in the upper 80s to mid 90s. The second warmest day was the 26th (Fig. 11), but it felt hotter with the dew points in the 60s (Fig. 12). Consequently, Bluefield hit 90oF on both of these days which is rare for them in June.
Figure 11. Temperature (oF) Image (June 26, 2007). Surface observations and isobars (black). Frontal analysis (blue).
Figure 12. Dew Point (oF) Image (June 26, 2007). Surface observations and isobars (black). Frontal analysis (blue).
Tropical Storm Barry (Fig. 13) brought beneficial rains (Fig. 14) to the region early in the month. The only rainfall record broken for the month was at Roanoke with 1.04 inches of rain on the 3rd (Barry). This broke the old record of 0.82 set in 1982.
Figure 13. Satellite and radar mosaic imagery, and surface frontal analysis on June 3, 2007.
Figure 14. Estimated precipitation amounts from NWS Blacksburg radar (June 3, 2007) from remnants of Tropical Storm Barry.
For most of the month, the area was peppered with isolated to scattered pulse thunderstorms during the afternoon and evening. Areas hit by one of these storms saw torrential downpours with rainfall rates of 2 to 3 inches. It was truly a hit-or-miss month for rainfall with monthly totals running about an inch or so below normal at WFO Blacksburg Climatic sites (Fig. 15). Averaging the rainfall totals from cooperative station across the area and June's monthly average rain was near normal (3.93 inches). The lowest rainfall value of 2.17 inches was reported at Radford 3N (RADV2) to a high of 7.83 inches at Lexington (LXGV2). Departures for the year were around 2 to 6 inches below normal with the worst being across the Southwest portion of the area and along the North Carolina and Virginia border.
Figure 15. Percent of Normal Precipitation (June 2007).
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As May's and June's temperature were above normal and as we got deeper into the Dog Days of Summer, one would expect July to be unbearably hot. This was not the case, as several pulse storms, a couple of cold fronts, and an upper level low kept average monthly temperatures near normal. The coolest departures (Fig. 16) were generally in our warmest locations (Southside Virginia). The only climatic site to see above normal temperature for the month was Bluefield (1.3oF).
Figure 16. Departure of Average Temperature (oF) from Normal (July 2007).
One reason why areas east of Bluefield had cooler monthly average temperatures was because of a back door cold front on July 12 (Fig. 17) that worked down the east coast and an upper level low over the region on the 25th. These two features kept clouds and rain in the area a little longer along and east of the Blue Ridge. There was one other front that crossed the area on the 19th (Fig. 18).
Figure 17. Temperature (oF) Image (July 12, 2007). Surface observations and isobars (black). Frontal analysis (blue).
Figure 18. Morning surface analysis on July 20, 2007
Ahead of these fronts, temperatures soared into the upper 80s to upper 90s with the warmest day occurring on the 9th (Fig. 19). Only one record high temperature was broken during the month and that was Bluefield's high of 92oF on the 9th. Once these fronts passed through the area, daily average temperatures fell to 5oF to 10oF below normal. On the 25th, an upper level low (Fig. 20) over the mid Atlantic region kept temperatures about 15oF below normal.
Figure 19. Temperature (oF) Image (July 9, 2007). Surface observations and isobars (black). Frontal analysis (blue).
Figure 20. 500 mb heights (m) July 24, 2007.
Rainfall for the month was generally below normal by 0.5 to 1.5 inches across the entire area (Fig. 21). Lynchburg was the exception with 2.80 inches above normal for the month. On the 17th, a slow moving storm dropped 2.59 inches of rain on the area (Fig. 22). Without this storm, Lynchburg's monthly rainfall total would have been around normal. All sites experienced one daily record rainfall day during the month. None of these daily record rainfalls occurred on the same day (Danville 1.87 inches on the 10th, Blacksburg 0.93 on the 11th, Roanoke 0.84 inches on the 17th, Lynchburg 1.63 on the 19th and Bluefield 1.54 inches on the 24th). Strangely enough, Lynchburg's highest daily rainfall for the month (2.59 on the 17th), was not a record for the day.
Figure 21. Percent of Normal Precipitation (July 2007).
Figure 22. Estimated precipitation amounts from NWS Blacksburg radar (July 19, 2007).
Each one of the fronts brought much needed rain to the area, but unfortunately they were accompanied by severe thunderstorms. Torrential downpours of 2-3 inches of rain with these storms produced mostly runoff but little flooding. More rain (Fig. 23-24) came with the upper level low and by the months end, yearly precipitation deficits were about the same as the beginning of the month (2 to 6 inches).
Figure 23. NWS Blacksburg Radar (July 25, 2007) displaying line of showers
moving slowly to the east.
Figure 24. Estimated precipitation amounts from NWS Blacksburg radar (July 25, 2007).
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Long-standing records for heat were obliterated in August 2007. August 2007 was the hottest August on record at 4 of the 5 climatic sites across Blacksburg's County Warning area. Among the 5 sites, no less than 62 daily records were set for both high maximum (32) and high minimum (30) temperatures combined. With the August heat wave centered further toward the mid west, the number of records set in our area was greatest in the west. Bluefield had 22 daily records set in August. On two separate days (16th and 24th), Bluefield topped out at 95oF which is the highest temperature for the month of August and second all-time for the entire year (96oF set on July 16, 1988). Roanoke had 15 records set, 6 for high maximum and 9 for high minimum. On the 9th, Roanoke recorded its warmest low temperature ever at 79oF. Blacksburg had 14 records set, 8 for high maximum and 6 for high minimum. Danville set 9 temperature records, 6 for high maximum and 3 for high minimum. Lynchburg only had 2 daily records set for high maximum. The cause of the heat wave was high pressure centered over the southeastern United States which did not allow any cold fronts to penetrate through the region. Figures 25 and 26 illustrate the frontal positions on a couple of the hottest days in August (9th and 16th).
Figure 25. Temperature (oF) Image (August 9, 2007). Surface observations and isobars (black). Frontal analysis (blue).
Figure 26. Temperature (oF) Image (August 16, 2007). Surface observations and isobars (black). Frontal analysis (blue).
The number of days in the month with a high at or above 90oF was record setting as well. Blacksburg was 90oF or greater on 12 days with the normal being 2. Bluefield was 90oF or warmer on 10 days with the normal being less than one. Danville had 29 days of 90oF or higher. Danville's normally only has about 14 or 15 day at or above 90oF. Of those 29 days, 5 days were at or above 100oF. The last time Danville was 100oF or warmer was on August 23rd, 2002. Roanoke reaches 90oF or higher 27 times with a normal around 8 days. Four of those days were 100oF or warmer. The last time Roanoke was 100oF or warmer was on July 6th, 1999. Lynchburg, with the least records set during the month, still had twice the normal number of 90oF or higher days at 16.
The average monthly temperature was the warmest on record for August in Roanoke (82.1oF), Danville (82.0oF), Bluefield (78.2oF), and Blacksburg (76.1oF). These average monthly temperatures for Roanoke, Bluefield and Blacksburg set new records for any month. The previous warmest month for these three stations was July 1993. Danville just missed being in this group by a tenth of a degree. With all these records, the average monthly temperatures across the area was 5oF to 7oF above normal (Fig. 27) . Roanoke's, Blacksburg's, and Bluefield's average daily temperature was at or above normal every day of the month of August (Graphs 6-10). For Danville and Lynchburg, all but two days were above normal.
Figure 27. Departure of Average Temperature (oF) from Normal (August 2007).
Graph 6. Roanoke, VA, Daily Max/Min Temperatures (oF) and precipitation amounts (inches) for August 2007.
Graph 7. Lynchburg, VA, Daily Max/Min Temperatures (oF) and precipitation amounts (inches) for August 2007.
Graph 8. Danville, VA, Daily Max/Min Temperatures (oF) and precipitation amounts (inches) for August 2007.
Graph 9. Blacksburg, VA, Daily Max/Min Temperatures (oF) and precipitation amounts (inches) for August 2007.
Graph 10. Bluefield, WV, Daily Max/Min Temperatures (oF) and precipitation amounts (inches) for August 2007.
It was the driest August on record in both Danville (0.60 inches) and Bluefield (0.65 inches). Blacksburg (1.65 inches) and Lynchburg (1.49 inches) had their 5th driest August. Roanoke (1.50 inches) had its 7th driest August. Preliminary data from NWS cooperative station across the area showed a mean of 1.66 inches. Normal for the area is around 3.63 inches for the month of August. Departures for the month were around 2 to 3 inches below normal or about 25 to 35 percent of normal (Fig. 28). Rain was limited during the month to mainly scattered afternoon and evening thunderstorms. Remnants of Tropical Storm Erin moved through the region on the 21st, but was moving too fast to help with the drought relief. By the end of the month, yearly rainfall deficits were 5 to 10 inches below normal. The southwest portion of the area was classified as being in a severe drought.
Figure 28. Percent of Normal Precipitation (August 2007).
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Labor Day weekend saw temperatures cool down into the 80s (Fig. 29), which was a welcome relief from the summer heat. This cool down only lasted a few days with daily temperatures jumping back above normal through the 13th. The 8th (Fig. 30) and 9th of September were generally the warmest days with temperatures reaching into the upper 80s to lower 90s.
Figure 29. Temperature (oF) Image (September 2, 2007). Surface observations and isobars (black). Frontal analysis (blue).
Figure 30. Temperature (oF) Image (September 8, 2007). Surface observations and isobars (black). Frontal analysis (blue).
On the 14th, a combination of a strong cold front and remnants of Hurricane Humberto brought much needed rain and cooler temperatures to the region. Temperatures following the front fell below normal by about 10oF with daily highs comfortably in the 70s. On the morning of the 16th, temperatures were in the 40s with some 30s across the mountains (Fig. 31). Bluefield had a low of 39oF, which was the coldest temperature recorded for the 16th of September. Typical of this Summer, the cooler temperatures did not prevail and by the 22nd, daily means were once again above normal (10oF to15oF). A slow moving front on the 27th brought temperatures back to normal levels by the end of the month (Fig. 32 and 33).
Figure 31. Temperature (oF) Image (September 16, 2007). Morning surface observations and isobars (black). Frontal analysis (blue).
Figure 32. Temperature (oF) Image (September 29, 2007). Afternoon surface observations and isobars (black). Frontal analysis (blue).
Figure 33. Dew Point (oF) Image (September 29, 2007). Afternoon surface observations and isobars (black). Frontal analysis (blue).
With a couple of weekly warm spells during the month, a few new records were set. Most notable was Bluefield, where daily high temperatures between the 4th and the 9th and the 23rd and 27th set new records. A total of a 11 new record highs and 6 warmest low temperatures were set in Bluefield during the month. Bluefield's average monthly temperature was 70.7oF (5.9oF above normal), which is also a new record. The old record was 69.2oF set in 1998. Bluefield is the youngest climatic site in the Blacksburg County Warning area. Bluefield's period of record starts in 1959. Our oldest site is Lynchburg whose period of record started in 1893. During September 2007, Lynchburg did not set any new records. Lynchburg's average monthly temperature of 69.7oF ranks 44th warmest of all time. Blacksburg (66.8oF), Roanoke (71.5oF), and Danville (72.9oF) also had a warm September. Their monthly average temperature ranks 5th, 6th, and 9th respectfully. When it was all said and done, September's monthly average temperature were 3oF to 6oF above normal (Fig. 34).
Figure 34. Departure of Average Temperature (oF) from Normal (September 2007).
Precipitation for September 2007 was hard to come by, as the area was dominated by a few dry surface high pressures. Preliminary data from NWS Cooperative stations across the Blacksburg's County Warning Area showed a mean of 2.21 inches of rain fell during the month. Normal amounts for September is around 3.81 inches. A cold front and Remnants of Hurricane Humberto did bring much needed rain to the area on the 14th (Fig. 35 and 36). Most of the area saw about an inch or two of rain from these two systems. The highest totals was in the Meadows of Dan area in Patrick County where 7 to 8 inches of rain fell (Fig. 37).
Figure 35. Afternoon surface analysis on September 14, 2007.
Figure 36. Satellite imagery, Mosaic Radar, and surface frontal analysis on September 14, 2007 (Remnants of Humberto).
Figure 37. Accumulative rainfall amounts from September 14, 2007 (Remnants of Humberto).
Another cold front on the 27th had the potential to bring more rain to the region with dew points in the 60s across the area. Unfortunately, the bulk of the rain and energy stayed to the north and tracked across the Ohio river valley. Only scattered locations in the New River Valley and Allegheny Highlands saw rain from this system (Fig. 38 and 39). Rainfall totals at the 5 climatic sites for the month were 2 to 3 inches below normal or about 40 percent of normal (Fig. 40).
Figure 38. NWS Blacksburg radar on the afternoon of September 27, 2007.
Figure 39. NWS Blacksburg radar on the evening of September 27, 2007.
Figure 40. Percent of Normal Precipitation (September 2007).
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