UPDATE 10:15 AM: The back edge of the rain area has cleared most of the New River Valley and will soon push through the Roanoke Valley. Expect breezy and cooler weather this evening into Tuesday, with lots of 40s lows. The next chance of rain arrives Wednesday with a possible coastal low forming from the remnants of Tropical Storm Karen. END UPDATE
UPDATE 5:30 AM: Heavy downpours and some gusty squalls are moving through the region this morning. At least some locations will likely go over 1 inch of rain. Rain will taper by early afternoon … But there are new indications that Karen’s remnants may trigger a coastal low with a new threat of showers by midweek, with much cooler temperatures. More on that once we get past today’s rain. END UPDATE
Rain is headed toward Southwest Virginia for Monday. While some of it could be heavy at times, it doesn’t appear that this will be the level of widespread torrential downpours that would have been possible if Tropical Storm Karen hadn’t gone kaput in the Gulf of Mexico. Still, some tropical moisture that was part of Karen — or, at least, the convection that formed 100+ miles east of Karen’s circulation — is working northward through Georgia on this Sunday evening at the same time a strong cold front is pushing east through the Tennessee and Ohio valleys. The lift of the front in newly moistened air, plus the tropical moisture from the south, plus some upslope effects as winds turn to the southeast for a time will lead to numerous showers and storms developing and moving into the area toward sunrise and continuing through the morning and into at least some of the afternoon. A general 0.50 to 1 inch rain would be the best guess at this point, with some locally heavier amounts. Wind shear is supportive of severe storms, but instability will be weak with clouds and rain dampening the heating. The best chances of strong to severe storms with locally damaging downburst winds or possibly even a weak, brief tornado would be east of the Blue Ridge. This rain/storm event is actually quite similar to the setup on Sept. 21, which produced widespread rain of .40 to 1 inch and some localized severe storms — even tornado warnings — east of the Blue Ridge.
Behind the front, we’ll have a couple of chilly mornings on Tuesday and Wednesday, with some mid to upper 30s lows possible west of Roanoke and low to mid 40s elsewhere. The overall pattern still suggests warm, dry weather will prevail over the next week or two, but there will be a classically autumn cool break for a couple of days with the passage of this front.