A frost advisory is out Sunday morning for Alleghany, Botetourt, Roanoke and Floyd counties and eastward. You will notice no advisories out for most of the New River Valley and westward — that’s not because it won’t be cold enough again Sunday morning for frost or freezing conditions, but that the National Weather Service in Blacksburg has determined the growing season is now over with Saturday morning’s freeze and that frost/freeze advisories will no longer be issued.
Somebody east of the Mississippi River and north of Interstate 40 is going to get an amazing amount of snow for late October about Friday or Saturday. We have a situation where a deep dip in the jet stream is about to deliver some very cold air for the season far to the south over the Eastern U.S, and also very likely spin up a strong low pressure system somewhere in the East. Some of the computer forecast model depcitions of the potential system have been absolutely jaw-dropping — like the one I’ve inset at left, from last night’s European model, which shows a 988-milibar low (29.2 inches of mercury) over Washington D.C. Friday evening pulling deep Arctic throughout our region. From the low’s track, strength and level of cold air, if this came to pass, it would probably dump several inches of snow in much of our region. BUT — most likely — this particular scenario will NOT come to pass. The more probable scenario, based on a growing plurality of forecast model runs (including the same European model for Saturday) and on the particulars of the pattern, favor a more inland path for the low and the likelihood of any heavy snow developing to our west and northwest in the Ohio Valley, possibly as far east as West Virginia, extending into the Great Lakes and part of the Northeast. The North Atlantic Oscillation is not solidly in a negative phase right now, which would mean that high pressure over Greenland would be present, and that often locks in a more coastal track for low-pressure systems. There also isn’t the upper-level low near Newfoundland that in winter often helps steer storms more along the coast rather than letting them go inland. And besides all that, it’s just exceedingly difficult to get everything to come together for a winter storm at this latitude in late October. It’s hard enough in January, but this early in the season, you have to get the perfect storm track and an extremely intense push of cold air with little room for variance. The odds are simply against significant snow in Southwest Virginia below 3,000 feet in October unless there are extraordinary circumstances.
All that said, the chance of seeing snowflakes across much of Southwest Virginia is pretty good next weekend. As the low moves north of us, cold northwest winds sweeping off the Great Lakes and over the Appalachians will squeeze out snow as the air is lifted, the common “upslope snow machine” we see with most cold front passages in the winter. That could mean a few to several inches of snow in West Virginia’s mountains, perhaps some white ground into the higher elevations west of Interstate 81 in Virginia. This time, the cold air will be deep enough that some flakes could get down to even the lower elevations — flurries even in Roanoke, possibly.
The details of this system are still too far out in the future to get very specific, and many could shift. A major shot of cold air next weekend appears to be the most certain aspect of it all. Before that arrives, we’ll shoot back into the 70s for highs Monday through Wednesday.