The seasons have shifted big time; dry weekend may turn rainy early next week, with blasts of early cold after that
Blacksburg’s low of 47 on Thursday morning was the fifth in a row below 50 degrees. That hadn’t happened since there were 12 in a row from April 5 to 16, including three below-freezing mornings. Before dropping into the 50s late Saturday night, Roanoke had gone 71 days without a low below 60 degrees. Friday, most likely, will make seven in a row. That reflects how much the weather pattern has turned recently from the first 8 months that have skewed warm — second warmest winter, warmest March, warmest spring and warmest July on record — and the coolness will likely get more extreme in coming days.
As forecast model runs have continued to portray a developing pattern that will funnel cold air from the most northern latitudes southward into the central and eastern U.S. over the next two weeks, it’s not the extreme nature of the cold I’m taken with — though it is possible there will be some record or near-record cold in there a day or two, possibly for us, more likely for the Great Lakes and Upper Midwest regions. It is the longevity that impresses me most, so early in the fall season. Once a strong cold front pushes in toward the middle of next week, there are likely to be multiple pushes of unseasonably cold air from near the Arctic Circle southward over the central Canadian prairies into the U.S. This is because strong high pressure, with unseasonably warm weather underneath, is building across the West Coast, western Canada and Alaska, as well as over Greenland. You may hear about an unusual return of summerlike warmth in some of those areas even as you hear about, and perhaps experience, an unusually arrival of wintertime chill in much of the central and eastern U.S. If some of the model forecasts verify, I could foresee 2-3 weeks of lows in the 40s most nights and highs in the 70s, with a few days mixed in with lows in the 30s in many parts of Southwest Virginia. At the upper end of extremes, the developing weather pattern (really, it’s already started, with this past week’s first push of Canadian air) has the potential to be a truly historic bout of September cold, with some early killing frosts in some areas of the Upper Midwest and Northeast (maybe even some frost for us) and some oddly early snowflakes in the Great Lakes and maybe even highs spots of the central and northern Appalachians. At the low end of the possibilities, we get a rather prolonged period of below-normal temperatures, rising to near normal just before each new push of Arctic/Canadian air arrives.
The weekend will see a slight reinforcement of the current temperature regime, reinforcing the generally near-normal 70s highs/50s lows pattern. Roanoke hit 80 on Thursday and 81 on Wednesday, and may get another low 80s high on Friday. After so many dry days, moisture will be slowly building toward the end of this weekend and early next week, and there are some growing indications of a potential storm system developing in the Ohio Valley and/or the South that could scoop some Gulf of Mexico and/or Atlantic moisture our way and squeeze it out into some rain through the early to middle part of next week. Forecast models still vary quite a bit on the details of this storm system’s development, but the Hydrometetorological Prediction Center is now suggesting amounts near 1 inch may occur Monday and Tuesday. Development of a substantial storm system this far south, leading to any kind of general rain shield as opposed to the spotty showery stuff we’ve seen with almost every system since May, would be yet another indication of just how much the weather pattern has changed.