1:40 PM | **Bitter cold on Thursday and Friday and then snow/ice problems on Saturday**
Paul Dorian
12Z GFS forecast map of 850 mb temperature anomalies for early Thursday afternoon featuring way below normal conditions in the Northeast US; map courtesy tropicaltidbits.com, NOAA
Overview
Another Arctic blast arrives in the Mid-Atlantic region late Wednesday night/early Thursday and it’ll be even colder than the last one. In fact, temperatures on Thursday and Friday are likely to be confined to the 20’s for highs and early morning lows on Friday could be in record-breaking territory in many parts of the Northeast US. This bitter cold, dense Arctic air mass will then begin to retreat on Saturday, but not before moisture reaches us from the Midwest and this potential collision could lead to significant snow and/or ice problems in the DC-to-Philly-to-NYC corridor before an eventual late day changeover to plain rain.
12Z GS forecast map of 500 mb height anomalies for early Thursday afternoon with deep upper-level low centered over SE Canada; map courtesy tropicaltidbits.com, NOAA
Today/Tonight/Wednesday
Clouds will persist through tonight as a couple of weak systems push towards the east coast and the combination of the two can produce a little bit of rain in the area later today and then a little bit of snow or sleet tonight. On Wednesday, temperatures will remain on the chilly side with some sunshine ahead of the next Arctic frontal system which passes through the region late tomorrow night and there can be some snow shower activity during the day and again tomorrow night.
12Z GFS surface forecast map for early Thursday afternoon featuring a tight pressure gradient (represented by the black lines (isobars)). A tight pressure gradient generally correlates well to strong winds. Also, the forecast map shows 1000-500 mb "thickness" values (dashed blue lines) which correlates well to temperatures and a value of "498" across Pennsylvania is unusual to see any time of the winter season let alone in the middle of December; map courtesy tropicaltidbits.com, NOAA
Arctic cold blast Thursday/Friday
The next Arctic front passes through the region by early Thursday and then the Arctic winds will howl as as an anomalous deep upper-level low builds into the Northeast US. Temperatures both Thursday and Friday will hold in the 20’s and strong N-NW winds could produce wind chill values of zero or below zero at times. Low temperatures early Friday morning can reach record-breaking territory in many parts of the Northeast US. Upper single digits are possible by early Friday in the NYC metro region, not far from 10 degrees in and around Philly, and near the 15 degree mark in DC. In addition to the bitter cold, there can be some snow shower activity on Thursday/Thursday night as the Great Lakes snow machine will be turned on full throttle. In fact, there can be a few heavier snow squalls that make it all the way to the coastal plain on Thursday in areas north of the PA/MD border.
12Z GFS surface forecast map for early Saturday morning with snow in blue, sleet/freezing rain in pink; map courtesy tropicaltidbits.com, NOAA
Late Friday night/Saturday/Sunday
Strong Arctic high pressure will be sitting right on top of the Mid-Atlantic region by Friday night and winds will calm down as a result Friday afternoon and evening. The Arctic air mass will then begin to retreat to the north early Saturday as this high pressure system shifts to a position off the coast, but moisture will arrive before the Arctic air has a chance to fully erode. As a result, snow could break out after midnight in the DC-to-Philly-to-NYC corridor and continue into early Saturday before then changing to a period of sleet and freezing rain. A cause of concern will be the fact that ground conditions will be quite cold following what could turn out to be 48 hours or more of below freezing temperatures going into the beginning of this weekend precipitation event. Eventually, milder air will win out all along the immediate I-95 corridor with the full retreat of the low-level Arctic air and plain rain is likely by later Saturday.
It is still too early to tell what the exact breakdown of snow, ice and rain will be early this weekend, but significant snow and/or ice accumulations are possible during the front end of the storm. It’ll stay mild for awhile on Sunday with more rain likely; however, there is the chance that it changes back to snow late Sunday as yet another shot of Arctic air arrives and then Monday will turn out to be quite cold. Stay tuned.
Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com