11:30 AM | *Severe weather threat tomorrow…”clipper” snow possible early Friday in Mid-Atlantic*

Jet streak predicted at 250 mb by 7pm on Wednesday; courtesy tropicaltidbits.com, NOAA/EMC

Overview
There could be a repeat performance on Wednesday of the strong-to-severe thunderstorm activity that was experienced in the Mid-Atlantic region this past Saturday.  In similar fashion to Saturday, temperatures will surge to record or near record levels on Wednesday and a powerful cold front will close in from the northwest.  This type of clash between spring warmth and winter cold resulted in numerous damaging wind reports on Saturday in the I-95 corridor along with a few isolated tornadoes - and the same scenario can take place later tomorrow all the way from the Mid-Atlantic region to the Tennessee Valley.  

Upper-level energy at 500 mb as predicted by 06Z GFS for 7pm Wednesday; courtesy tropicaltidbits.com, NOAA/EMC

Surface-level Details
High pressure has pushed off the east coast and this new positioning has allowed low-level winds to turn to a more south-to-southwest direction and milder air is now flooding into the Mid-Atlantic region.  This warm up will accentuate on Wednesday as temperatures soar to record or near record territory – surpassing the 70 degree mark in Philly and New York City and approaching 80 degrees in DC (record on Wednesday in Philly is 76 degrees set in 1972). In addition to the warm up, low-level moisture levels should rise on Wednesday ahead of a strong cold front and this will help in the destabilization of the atmosphere and contribute to the overall threat of thunderstorms.

12Z NAM predicted atmospheric sounding for Lancaster, PA for tomorrow afternoon

Upper air details
In the upper part of the atmosphere, a vigorous wave of energy will drop into the Central Plains and a powerful jet streak at 250 mb will head into the eastern states.  This scenario means there will be a lot of wind to tap into aloft and this suggests damaging wind gusts will likely be the primary threat later Wednesday from thunderstorm activity.  However, hail can certainly become a player as it did last Saturday and there can be a few isolated tornadoes later tomorrow in the expected very unstable environment.  In fact, the 12Z NAM forecasted sounding at Lancaster, Pennsylvania shows “tornado” as a possible hazard type (far right) based on the expected unstable atmosphere.

06Z GFS surface forecast map for Wednesday 7pm; courtesy tropicaltidbits.com, NOAA/EMC

 “Clipper”
Following the passage of the strong cold front, it’ll turn colder on Thursday with brisk NW winds.  A fast-moving (“clipper”) system will then drop southeast from the Great Lakes region into a deepening upper-level trough along the east coast.  This “clipper” system is likely to throw some light snow into the DC-to-Philly-to-NYC corridor early Friday and then there will be a reinforcing shot of cold air to follow as we begin the weekend.  As has been the case for much of the winter, this next shot of cold air will not last too long and a warm up begins by early next week. 

06Z GFS surface forecast map for early Friday afternoon; courtesy tropicaltidbits.com, NOAA/EMC

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com