UPDATE 1:50 PM: Heat wave meets stormy end after today’s extreme heat; showery, much cooler days ahead
UPDATE 5:25 PM: Roanoke’s high hit 102 today, breaking another daily record, topping the 101 from July 8, 1977. Storms continue to develop along a cold front pushing into West Virginia and Kentucky. Storms in the Charleston-Huntington W.Va. currently are likely to move across Southwest Virginia later, with damaging winds and heavy rain possible. It’s not a derecho, but more typical summer storm clusters, but there is potential for at least localized wind damage to trees and power lines. Keep an eye on Radar / Future Cast in the right margin of this blog, and on the National Weather Service-Blacksburg web site for the latest warnings. END UPDATE
UPDATE 1:50 PM: Severe thunderstorm watch issued until 10 p.m. for localities north of U.S. 460 corridor (Blacksburg-Roanoke-Lynchburg). Expect this to be expanded south later as storms fire along an advancing cold front cutting into this extremely hot air. Damaging winds are the main threat in severe storms this afternoon, along with some hail. END UPDATE
UPDATE 1:35 PM: Roanoke has already reached100 degrees early on this Sunday — with sunshine continuing, plus downsloping westerly to northwesterly winds and some compressional heating ahead of the coming cold front, we could easily see a high of 102-105 this afternoon. 105 is Roanoke’s all-time record high, set twice in the 1930s and again Aug. 21, 1983. A severe thunderstorm watch is expected soon in West Virginia — this will be what we keep our eyes on for later today as it moves southward ahead of the cold front. END UPDATE
Roanoke’s official high through 5 p.m Saturday was 102 degrees, the third triple-digit reading in the last 10 days, which is the hottest period of that length in the Star City, based on average high temperature, since July 12-21, 1977. With three 100-plus days, six 97-99 days and one other at 94 (last Monday), the June 28-July 7 period has had an average high of 98.7 degrees. The 1977 period listed above averaged 98.8, with five 100-plus days. A high of 93 Sunday would tie this 11-day heat wave with a July 12-22 period in ’77, and 94 would make this one a tenth of a degree hotter. The high is projected to be near 100 for Roanoke on Sunday. Roanoke averaged 99.5 degrees over 12 days in 1930, and this period will not exceed that. I will check to see if there were any similarly hot 11-plus day periods during some of the blistering hot early-mid 1950s summers.
The biggest reason it will not surpass 1930 is that Sunday is very likely the last day of the ongoing heat wave, and maybe the last 90-plus day for a week or more. A major weather pattern change is developing that will rearrange the weather features that have led to so much extreme heat and mayhem east of the Rockies over the last 2 weeks. The jet stream is dipping southward into the Northeast U.S. — this will push a cold front southward that will collide with our heat, leading to a potential for severe storms Sunday afternoon evening just about anywhere in Virginia, and then only a little farther south on Monday. As is typical for midsummer cold fronts, it is expected to get hung up near or just south of us through the first half of next week, and that will provide a focusing mechanism for shower and storm development. Passing low-pressure waves along the front will have the potential to trigger repeated rounds of showers and storms the next several days as they lift Gulf of Mexico moisture over the stalled front. The Hydrometeorological Prediction Center is showing the potential of 2 inches or more of rain through Thursday over about the southern half of Virginia. I’m a little leery about jumping on those totals for now, knowing how difficult it often is to pinpoint exactly where a front will stall. The potential is certainly there for that kind of rain, and in any event, showery, much cooler weather than we’ve seen appears to be in the offing through midweek. Highs on Monday may have some chance of clipping a sticky 90 from Roanoke south and east, but by Wednesday may be struggling to make 80.