[Beautiful satellite image of developing storm showing extensive moisture connection to the Gulf of Mexico]
A powerful nor’easter will greatly impact the Mid-Atlantic region from DC-to-Philly-to-NYC beginning tonight and lasting right through tomorrow night. This storm has already affected the Deep South with widespread snow and ice and - when all is said and done - it could rival some of the all-time great storms in terms of its extensive impact from the Deep South to northern New England.
It looks like the storm will come in three different phases in the Mid-Atlantic region. The first phase on the front end will feature heavy snow with 1-2 inch per hour rates producing several inches of accumulation. The second phase will see a changeover of the snow to sleet, freezing rain, and/or rain from around Route I-95 to points east, and possibly as far inland as some of the northern and western suburbs of the big cities although that is not a certainty. It is entirely possible that the storm remains as all-snow in some of the northern and western suburbs which, of course, would help out with snow accumulation amounts. The third phase on the back end will see a changeover of any mixed precipitation back to all-snow and this “wrap around” snow in the “cold conveyor belt” region of the storm on its northwest flank will add significantly to the overall accumulations throughout the region.
The snow in the first phase will begin in DC early tonight (by ~7pm), in Philly during the late evening (by ~10pm), and then around midnight in NYC - and the snow will stick in a hurry given the very cold ground conditions. The middle phase featuring the sleet/freezing rain/rain – at least from around Route I-95 and points east - will take place during the day on Thursday and this precipitation will come down at varying rates of intensity. By tomorrow evening, as the storm passes by off the Mid-Atlantic coastline, colder air will return and any mixed precipitation will change back to all-snow and continue until after midnight in an impressive “cold conveyor belt (CCB)”. The CCB region of the storm (northwest flank) is also known as the "deformation zone" and it is often characterized by "bands" of snow which can come down hard at times and even include some possible "thunder snows". Winds will become a factor gusting up to 25-35 mph as we progress through Thursday and Thursday night. The winds at the coastline could gust past 40 mph later tomorrow and tomorrow night.
In terms of snowfall accumulations, there will be a rather sharp gradient from northwest to southeast, but significant accumulations will occur throughout the DC, Philly and NYC metro regions. In general, these metro regions will likely end up in the 8-14 inch range, but even higher amounts are possible in the northern and western suburbs that remain as primarily snow on Thursday during the middle phase of the storm.