Tuesday, Dec. 15, 2020
Seems like the thoughts of snow have brought me out of hibernation. So, here come some thoughts on yet another one of our rain/sleet/snow situations…
In general, an active upper air trough will swing out of the Rockies through the Ohio Valley to the east coast by late tomorrow. Ordinarily, that would bring us some rain under the current temperature setup. But, this system features a big twist. A big lobe of energy has dropped into the far southern part of the system. That piece of energy will gradually take control and become the primary driver of the spectacular nor’easter expected to drop a foot or two of snow from West VA, PA and to New England by tomorrow night.
Meanwhile, we’ll be left with a dying system over the Ohio Valley. Thus, total precipitation will probably amount to a quarter-inch or less. But, in what form will it fall?
One important thing – all models agree that temperatures around 5000 feet above the surface will stay below freezing. That definitely keeps snow in play. Also important is when the dying upper air system trudges up the Ohio River, temperatures in the lower atmosphere will warm. That pushes the odds for rain/drizzle higher.
Put a line about 20 miles south of the Ohio River.
If you live south of that line, you’ll see a rain/snow mix after 3 A.M. changing to rain after an hour or two. By daybreak, it’ll be rain/drizzle through midday. Possible flurries late afternoon/evening.
For the rest of us, here’s how I think it’ll work – Clouds will thicken this evening while local temperatures drop into the mid thirties. Around 3 A.M. some snow should begin. Mixed with rain and/or sleet, it’ll continue until about daybreak. Little accumulation on roadways, but grassy areas could see 1″-2″ locally. Up to 3″ farther north of the river.
After daybreak, we’ll see periods of light snow, rain and mostly drizzle through the morning. No additional accumulation is expected. In fact, most of the overnight snow should melt away. Snow flurries will be likely again as colder air arrives late afternoon into the evening