The potential continues for an important accumulating snow event on Thursday and Thursday night in the Mid-Atlantic region, but the question is still open as to whether this will be a moderate storm or something more significant. The ingredients that are on the playing field do indeed have the potential to generate a major snowstorm in the Northeast US, but the details of the storm evolution are still to be ironed out. The ingredients that will be part of this developing storm system include the following: (1) an active sub-tropical jet [see water vapor image above] (2) vigorous energy in the upper atmosphere dropping southeastward from western Canada (3) an associated strong upper-level jet streak (4) an upper level low over southeastern Canada that will force that vigorous energy towards the east coast and (5) strong high pressure situated to the north that will be anchoring an Arctic air mass.
It appears that initially there will be multiple low pressure centers in the eastern US on Thursday and then one of these will consolidate near the Mid-Atlantic coastline as the upper level trough approaches the eastern seaboard. The exact timing and phasing of this surface system will determine the extent of the snowfall in the Mid-Atlantic region later Thursday and Thursday night. In terms of the timetable for this upcoming event, while there can be some snow as early as late Wednesday night and Thursday morning, the heaviest snow would likely occur from late Thursday afternoon through Thursday night. In terms of precipitation type, while it is possible that some rain mixes in at the onset of this storm, the majority should fall as snow from the I-95 corridor to points north and west as it will become increasingly colder. In fact, snow can be expected all the way to the coastline as it becomes colder during the duration of the storm. Snow-to-rain ratios, which are normally around 10-to-1, will likely become as high as 15-to-1 in places like NYC as colder air takes over in the upper atmosphere during this storm. Very preliminary snow accumulations estimates are as follows: coating to 2” in the northern and western suburbs of Washington, DC, 2-5” in the Philly metro region, and 5-8” in and around NYC. Bitter cold air follows on Friday and Friday night with low temperatures by early Saturday morning perhaps near 0 degrees in the Philly metro region and even below zero near NYC. Looking ahead, another bitter - and perhaps record-breaking - cold air outbreak will reach the Mid-Atlantic region around Tuesday of next week. A detailed breakdown of the 12Z GFS model run and how it handles all of these ingredients can be viewed in the latest video discussion (below). One final note, in terms of playoff football, temperatures will probably be around 20 degrees at kickoff time for the Eagles game on Saturday in South Philly against New Orleans.