A powerful cold front will sweep towards the east coast on Wednesday and its going to make for some wild weather in the Mid-Atlantic region over the next couple of days.  Temperatures will surge ahead of the front on Wednesday to 60+ degrees in many parts of the Mid-Atlantic on stiffening south-to-southwest winds, and there can be a shower or two during the morning and early-to-mid afternoon hours.  By late in the afternoon, the heavy showers and possible strong thunderstorms associated with the front will approach the I-95 corridor from DC-to-Philly-to-NYC. 

Heavy rain will fall tomorrow evening in much of this area with 1 to as much as 3 inches possible by early Thursday.  All of the key ingredients are in place for a synoptic-type heavy rain event with a strong low-level jet oriented parallel to the boundary zone along with strong low level convergence and upper level divergence.  This threat for heavy rain is important given the fact that the ground is still quite frozen just beneath the surface following the recent extreme cold and despite the fact that surface temperatures are now above freezing.  Heavy rains over frozen ground can produce high runoff rates so flooding is certainly possible on streets and in streams by later tomorrow night.

As far as the threat for severe weather is concerned (e.g. winds, thunderstorms), there is a powerful jet streak associated with a vigorous upper-level short wave that will swing through with the frontal system.  The 3-hourly pressure falls just ahead of the front should be on the order of 3 millibars and the 3-hourly pressure rises post-frontal passage also on the order of 3 millibars.  The 12Z NAM model run (below) features a strong upper-level wave at 500 millibars and also a strong jet streak at 300 mb as of tomorrow evening.  There also is a strong low level jet ahead of the storm system.  The GFS model is suggesting winds just a few thousand feet above ground level could exceed 75 mph.  

All of this will have to be monitored closely during Wednesday, but the potential is there for damaging wind gusts, strong thunderstorms and especially for heavy rainfall with possible localized flooding.  Much colder air follows for the Mid-Atlantic on Thursday with temperatures probably peaking early in the day and then dropping through the 30’s during the afternoon hours.  Video discussion available at http://thesiweather.com/category/phl/