UPDATE 8:10 PM: The severe thunderstorm watch has been cancelled for Southwest Virginia as the storms have moved south of the region. Northeast winds behind a cold front are now bringing cooler air into much of the region. END UPDATE
UPDATE 3:25 PM: Severe thunderstorm watch until 9 p.m. for much of Southwest Virginia, including the Roanoke and New River valleys. Afternoon heating, abundant moisture and a slow-moving, diffuse cold front are working together to trigger showers and storms in our region. One line of storms is slowly moving through Botetourt County, while also building back to the west, and may enter the Roanoke area within the next hour or two. Locally damaging winds and some very heavy downpours are the primary storm threats this afternoon. END UPDATE
This historic heat wave is over for Southwest Virginia. For Roanoke, it was 11 days averaging 99 degrees–4 days over 100, 6 97 to 99 and 1 at 94. It appears to be the most severe heat wave of that length or longer since 12 days averaged 99.5 degrees in 1932. The last heat wave of similar intensity was in 1977, which actually had a couple different periods separated by a couple of cooler days. I’ll get back to examining this heat wave historically.
If the sun slips out enough between showers on Monday, it might hit 90 degrees in a few places from the Roanoke Valley southward and eastward. The rest of the week is likely to have high temperatures ranging from the 70s to mid 80s. Even Roanoke may struggle to make 80 at midweek, as cooler air settles in from the north, repeated rounds of showers and storms move through or nearby, and the core of the “heat dome” high pressure system relocates to the western U.S.
The cold front is only sluggishly settling southward overnight just north and west of us, and will only slowly slip south of us the next few days. It will serve as a focusing mechanism for repeated rounds of rain and some storms through the week. That’s why the Hydrometeorological Prediction Center has us in the bright colors depicting 2-5 inches of rain through Friday. It probably won’t be smoothed-out lines like the map shows, but more spotty/streaky, with some very heavy bands of flash flooding rain while others get lesser amounts. But this map gives an idea of the potential for rain this week as waves of low pressure and clusters of showers and storms move near and along the stalling front. The threat of severe weather — locally damaging winds, primarily — will remain overnight and Monday, (the Storm Prediction Center has circled us in a slight risk of severe weather) but it appears likely to be localized as it was Sunday afternoon (several damage reports from Bedford County) rather than widespread high winds. But we’re all going to be a little on edge about power outages with the June 29 derecho fresh in our minds, and there may well be some as even modest gusts in the 40-50 mph can loosen some limbs weakened by the derecho.