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Tuesday, 11:55 a.m.
Once again it's snow around Philadelphia, and it is snowing about as hard as it did Sunday when a quick 6-10 inches of snow fell on portions of northeastern Maryland, northern Delaware, southeastern Pennsylvania and parts of New Jersey. The snow amounts won't be quite as prolific with this 'storm,' but several more inches will have fallen by the time it moves away early this afternoon.
I hesitate to call this a storm, as it really isn't. It's more of an upper-level feature that is pulling moisture over a cold front and squeezing for all it's worth before darting off the mid-Atlantic and New England coasts. Nevertheless, this feature is producing snow, and it will do what any storm would do as it departs, and that is pull colder air in behind it.
After sundown, it's a 72-hour period of cold and dry for much of the country. Look at the following graphic, which is from the 12z Dec. 10 GFS, and it's a 72-hour precipitation total from this evening through Friday evening:
The precipitation that shows up from Missouri to northeastern Texas is all Friday, mainly Friday afternoon, and it's with the next storm that will be taking shape Friday night and Saturday. Take that off the forecast chart, and most of the country from California to Connecticut is dry - and cold, too.
Of course, there are a few things worth noting on that graphic. Look, for instance, at Florida. Not the precipitation showing up along the Atlantic coast. As high pressure slides into the lower Mississippi Valley Thursday, the northeast flow it will generate off the Gulf Stream will produce a few spotty showers near the coast and offshore.
You may also see the precipitation showing up around the Great Lakes and even back into parts of the Midwest. That's a combination of several things, the first of which is a weak disturbance now moving into Michigan toward upstate New York. Here's the 12z Dec. 10 NAM 700mb relative humidity forecast for this evening:
You can see all of the deeper moisture speeding away from the New England and mid-Atlantic coasts, but there's that little tail of moisture rotating through the eastern Great Lakes at that time. It will produce a little snow, but not a lot.
Right behind it, there is still another feature zipping across the Plains toward the Midwest, and it, too, will produce a little snow. This afternoon, the snow will slide out of Montana toward South Dakota, then tonight it will show up in southern Minnesota and central and northern Iowa, reaching southern Wisconsin and northern Illinois largely after midnight. From there, it will bring snow through southern Michigan and the northern Ohio Valley tomorrow, then into upstate New York, where it will sort of become 'lost in the sauce' of lake-effect snow.
Separately these two features will pull colder air into the pattern, with tomorrow being colder than today in the East and Thursday being the coldest. That coldest day in the Midwest and Great Lakes could well be tomorrow.
A third aspect of the precipitation showing up around and downwind of the Great Lakes is, of course, your more traditional lake-effect snow off Lake Michigan, Lake Superior and lakes Erie and Ontario. Given the higher snow-to-liquid ratios in lake-effect snow, it's conceivable someone winds up with more than a foot of snow through Friday from northeastern Ohio to southwestern New York as well as in the Tug Hill plateau area.
Lastly, you will note a return of moisture to the Northwest, particularly from the Cascades on west. Much of that will be in the form of showers late Thursday into Thursday night, with some snow in the Cascades.
It should also be pointed out that while cold will dominate from the Plains on east, it will begin to moderate over the western Dakotas back through the Rockies into the West. In fact, here are the projected temperature anomalies for Friday:
It's no heat wave, mind you, but considering how brutally cold it was for the past week, even normal will seem balmy!
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