UPDATE 9:30 AM, 9/20: Clouds kept low temperatures well above forecasts on this Thursday morning, mostly upper 40s to mid 50s — only 58 at Roanoke. The next 3 days will be a little warmer, 70s highs, 50s lows, mostly, maybe even a few low 80s by Friday, before the next major cold front arrives Saturday night with the coldest air we’ve seen since spring. END UPDATE
The rain is gone, and a cold front is sweeping through overnight that will sweep out the brief return to mugginess we have experienced. This will return us to the cool, dry Canadian air we experienced much of last week. Highs will struggle to hit 70 Wednesday, and morning lows on Thursday will likely be in the 40s across almost all of Southwest Virginia. We’ll warm up briefly back to near 80 for highs and mostly 50s for lows by Friday and Saturday before a stronger, though mostly dry, cold front arrives over the weekend. This front will be strong enough that Wisconsin and Minnesota may well see some accumulating snowfall by Saturday. Here, it will drive the lows back into the 40s, and perhaps by Monday and Tuesday morning, even some 30s. There may be even a chance of scattered frost in some of the colder spots west of Interstate 81 — as of now, doesn’t look like a widespread frost threat, certainly not a killing frost. The Climate Prediction Center’s 6-10-day temperature outlook puts the best likelihood of colder than normal temperatures right smack over us. The pattern remains favorable for repeated shots of cool, dry Canadian air, as hot high pressure dominates the West Coast, its clockwise rotation driving the colder air masses out of Canada into the central and eastern U.S. An early fall can resume after a brief interruption. You will be seeing more and more streaks of colors in the trees with cool mornings ahead.