While the calendar says Winter begins on December 21, Mother Nature wants to start things off a bit early across the Mid-Atlantic. SNOW is possible late Sunday Night into Monday — and it COULD accumulate IF everything aligns correctly! However, it’s not too uncommon for this region to see snow in the beginning of December as we’ve seen some decent systems produce several inches of snow.
Let’s get to the easy part of the forecast first! Rain will move into the region late this evening and continue through the overnight hours. Rain will end by early Saturday morning with rainfall totals ranging from 0.5 to locally 2+ inches. Some minor flooding is possible along with the potential for minor river flooding. Temperatures on Saturday will rise into the low to mid 50’s east of the Blue Ridge and 40’s in the mountains with gradual clearing by late morning.
We often talk about the “northern” and “southern” branch of energy and you can get decent wintry events if “phasing” occurs, especially if cold air is present. This image shows the 500 mb vorticity (up in the atmosphere.) It shows two pieces of energy attempting to phase. The disturbance across the Great Lakes and Ohio River Valley Region would help to drag the developing area of low pressure in the southeast much closer to the coast.
Also, some models are showing a pretty decent cold air mass with weak high pressure to the north. “Overrunning” precipitation would develop (and some of our best small to medium events have been from overrunning) where precipitation would move over the colder air at the surface. IF this comes in during the night, snow would be favored. However, during the daylight hours in early December and not a truly cold air mass to work with, the sun angle can push temperatures several degrees above freezing and limit any accumulation from occurring.