12:00 PM | **Severe weather threat this afternoon; especially, south of the PA/MD border..."clipper" snow threat early Friday**

High-resolution forecast map for 2pm with line of storms approaching DC and Philly; map courtesy Weather Bell Analytics, NOAA

Overview
March is starting off on a very active note with the threat for severe weather coming to the I-95 corridor this afternoon and possible “clipper” snow early Friday.  Today’s threat comes from the combination of an approaching strong cold frontal system plowing towards the east coast, strong upper-level winds and vigorous energy, and an unusually warm, humid air mass at low-levels of the atmosphere.  The severe weather threat this afternoon is greatest in those areas that are currently seeing some sunshine poking through the clouds (e.g., DC metro region) as this will act to destabilize the lower atmosphere.  The main threat this afternoon will be damaging wind gusts of up to 65 mph or so, however, just as was the case last Saturday, there is the chance for hail and a few isolated tornadoes; primarily, south of the PA/MD border.  After a very windy and colder day on Thursday, a “clipper” system is likely to generate some snow in the Mid-Atlantic region early Friday and there can even be some small accumulations; primarily, north of the PA/MD border.  

The latest visible satellite image shows clearing skies have advanced northward into south-central PA ahead of the incoming powerful cold front.  In those areas where clearing occurs, the chances for severe weather will increase due to lower atmosphere destabilization; image courtesy Penn State eWall

Afternoon severe weather threat…greatest threat south of PA/MD border
It looks like a line of strong-to-severe thunderstorms will come through the DC metro region between 1 and 3 pm and between 2 and 5 pm in the Philly metro region.  This line is likely to be less intense towards the NYC metro region due to thick cloud cover there that will limit lower atmospheric destabilization over the next couple of hours.  Sunshine is already breaking through in the DC metro region and there can be some brightening this afternoon up towards Philly and southern New Jersey.  Any thunderstorm later today can contain damaging wind gusts of up to 65 mph or so, downpours for 30-45 minutes, and perhaps even some hail.  In addition, it is not out of the question that a few storms spawn tornadoes in the I-95 corridor later today.  The actual surface cold front should come through in the overnight hours and winds will intensify dramatically in the wee hours of the morning.
  
“Clipper” snow early Friday…accumulation (small) threat greatest north of PA/MD border
Following the passage of today’s strong cold front, it’ll turn colder late tonight and on Thursday with strong 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 produce some snow in 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. Indeed, there is a chance for small snow accumulations early Friday from this “clipper” system; primarily, in areas to the north of the PA/MD border.  

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com