UPDATE 11:40 PM, 11/25: Cold morning again Monday, then quick rebound to near 60 by Monday afternoon; maybe a snow flirtation on Tuesday
UPDATE 11:40 PM, 11/25: Another cold morning on Monday, though likely not quite as cold as Sunday — the coldest morning yet this season, officially, with a 20 low at Blacksburg and a 26 low at Roanoke, and even colder in some spots, as low as 16 in Chatham (yes, in Southside) and at Troutdale in Grayson County. Monday will see highs in the 50s, with a few spots possibly reaching 60. There will still be some rain showers early Tuesday as an upper air disturbance and front push through, with some snowflakes not out of the question especially northwest of Roanoke, especially at higher elevations. It will be a quick shot of light precipitation with surface temperatures above freezing at most locations, so likely no big deal in our neck of the woods. The week beyond this looks to have seasonable temperatures for the most part, with lots of 50 highs (40s on Wednesday, right behind the cold front) and 20s/30s lows. A growing concern in much of Virginia with long-term dryness and some breezes is enhanced fire danger — beware. END UPDATE
The Arctic shot will make for a cold Sunday — upper teens to mid 20s across much of Southwest Virginia by Sunday morning, recovering only into the 40s (and maybe some cold spots not that warm) under full sunshine Sunday afternoon. Doesn’t look like the wind will die down enough to unleash radiational cooling full throttle, which could have sent everybody deep into the teens. Temperatures recover into the 50s to low 60s by Monday as winds turn southwesterly ahead of the next wave in the atmosphere.
This next upper-level impulse will be a little bit interesting to snow fans because it will be pulling a little Gulf of Mexico moisture atop cold air forced southward by high pressure to the north. It’s a fairly common setup we refer to as “overrunning” that often produces wintry precipitation in Southwest Virginia. In this case, it appears for now that air cold enough to support a wintry mix on Tuesday will be just north of most of Southwest Virginia, in West Virginia and western Virginia north of I-64. The map at left is from Saturday’s 12Z GFS for Tuesday morning, and shows the 0C/32F line (the blue one) at 850 millibars (roughly a mile up) from southern West Virginia to near Alleghany County and Lexington to the Charlottesville area. The green represents precipitation in the last 6 hours prior to 7 a.m. Tuesday — light green is under .10 inch. Anything north of the blue line would have the potential to have some snow, but as you can see, precipitation amounts are likely to be light. Considering this and marginal surface temperatures, no large-scale winter storm is expected, but the cold air cuts in just enough that some snowflakes may be possible Tuesday, more so the farther north and northwest you are, and the higher up you are, relative to Roanoke. This wave squirts out to sea quickly, and a second shot of Arctic air pours in behind it, probably not quite as sharp as this weekend’s. Beyond that, it looks like for several days after low pressure in the Pacific Northwest and in the central U.S. will dominate the pattern, which may mean milder temperatures gradually move in until, possibly, the central U.S. low slides into Canada and pulls down another slug of Arctic air by the early days of December. There is plenty of cold air parked over widespread and dense snowpack in Canada and over the pole in Siberia, it will just be a matter of when and whether the weather pattern aligns to pull it into the eastern U.S. as we begin moving into winter in earnest in the month of December.