UPDATE 9AM: Some showers are already occurring in parts of Southwest, Western and Southside Virginia on this Sunday morning. These will be intermittent through Monday morning, with heavier bands of rain and some storms developing late Monday into Tuesday. Latest radar linked here. END UPDATE
UPDATE 11:45 PM, 9/15: Nothing much to update, with rain expected to roll in Monday and Tuesday. Forecast totals from the Hydrometeorological Prediction Center top 3 inches by Tuesday evening from the New River Valley west, with 2-plus inches areawide. Some showers may develop Sunday afternoon and evening, but the heavier rain likely doesn’t arrive until the latter part of Monday into Tuesday. Cooler air still headed our way by midweek — highs may stay in the 60s many places Wednesday, with lows in the 40s just about everywhere by Thursday morning. END UPDATE
This long stretch of pleasant, dry weather has another day or two left in it before it comes to a screeching halt — the dry part, that is.
High pressure behind the latest reinforcing cold front, passing through overnight with little notice, will move east of us by Sunday. This, combined with approaching low pressure from the southwest, will turn winds to the southeast, a critical element in what looks to be a significant to heavy rainfall across all of Southwest Virginia by Monday and Tuesday. That southeasterly wind will bank Atlantic moisture against the gradually rising terrain of the western Piedmont and the steeply rising terrain of the Appalachians, squeezing out some showers as early as late Sunday. As the low approaches from the southwest, it will provide a healthy helping of Gulf of Mexico moisture. This is a classic pattern for large cool-season precipitation makers in the Southeast, Appalachians and East Coast regions. The storm system will even have a northern and southern element “phasing” into a more complex East Coast storm, though this may not happen until it is just past our region. Expect Monday and Tuesday to be rainy days, maybe not constantly but at least frequently, with rainfall amounts likely to top 1 inch regionwide. The Hydrometeorological Prediction Center is expecting about 2 inches or more through most of the area, and some models have suggested 3-plus will be possible. This should be the widespread soaking that Isaac’s remnants and several other summer systems have not been.
A strong Canadian cold front will push in behind the rain, bringing the first of several blasts of air from the northermost latitudes over the next couple of weeks. This shot will probably not be the biggest of the series, though Thursday morning’s temperature may be in the 40s across the region, similar to this past Tuesday, with maybe a few 30s, all well below normal. Dry air behind the front and sunny skies will allow daytime highs to warm into the 70s, though Thursday may struggle to make that in some locations west of Roanoke.