Short Version: I’m upping my forecast… for 6 to 12″ of snow along and west of I-95. However, the IF-THEN element still holds. IF we stay all snow, THEN I’d go higher… 10-18″, perhaps as much as 20″. But it does not appear we’re gonna pull this all-snow stunt off. Rather, warm air will get dragged into the storm aloft (~5,000 ft up) during the day Thrs, and change this over the a mix or rain, cutting into snow totals. Snow arrives tonight between 7 and 10 pm, and will fall heavily into the morning. Snow will then change over to sleet, freezing rain, and rain from southeast to northwest during the morning, altho far nrn and western areas may very well stay all snow. In these all-snow areas, at least 10″ of snow is probable. During the afternoon, the trailing “parent” upper-air low will swing thru, and this will act to restart the snow across most of the region in the late afternoon, lasting into the evening… dropping several more inches of snow east of the Blue Ridge.
Part 1: The first part of the snow is a slug of moisture coming up the coast ahead of the low, which will run into the cold air entrenched over the region. This snow will start between 7 and 10 pm tonight, and rapidly intensify. This moderate to heavy snow will last into Thrs morning, and will account for 6 to 12″ of snowfall across much of the region.
Part 2: As the low comes up the coast, warm air will get pulled into the system… and a change over will likely occur along the I-95 corridor. Most of the latest models show this happening by ~ 10am – Noon. The mix/rain lasts into the afternoon, and if this is correct, not only would we not see any add’l snow accumulation, but we’d lose snow due to melting and settling. If we stay all snow (and areas to the north and west may very well stay all snow), then another 2 to 4″ would fall.
Part 3: The new wrinkle… as the upper-air “parent” batch of energy swings thru during the afternoon, the models now show a second, new area of low pressure forming just east of the Delmarva. This is a huge wild card, and would result in snow redeveloping and intensifying, especially east of the mountains. Could also be sleet, depending on how much warm air we’ve dragged into the storm. This part of the storm would start Thrs afternoon and last into the evening, ending ~ Midnight. We’re gonna have to keep a real close eye on this.
Well, I’ll probably tweak this a bit when the other “later” models roll in, but I think this is a pretty good bet. 6 to 12″, and if we stay all snow then expect more. Could top it off with another bonus round Thrs eve.