Monday PM Disco- Wednesday Nighrt Washout!

Synopsis

High pressure sitting atop the state will slide out tomorrow as an intensifying cyclone approaches. Gusty warming winds will lead the precipitation, which will hit as rain overnight Tuesday, and will persist as the upper level low remains stagnant over the Northeast.  Rain will turn to light snow after a brief break Wednesday afternoon, and then light snow will persist into Friday, leaving for a rather damp and dreary week. Beyond this, a strong trough aloft will help escort a rush of cold Canadian air for the weekend.  

Short Term (Monday Night Into Wednesday Afternoon)

High pressure sitting atop the Northeast will progressively slide toward Nova Scotia as overnight tonight, leaving for partial cloud cover in the late night to Tuesday morning hours. A strong cyclone (TWC's  Rocky) over the south central Pains will continue to intensify as the upper level cutoff makes a beeline toward the Northeast. A strong pressure gradient will develop over the state by 21z Tuesday, and rain will begin to fall in SW PA shortly before 18z Tuesday (with surprisingly a strong consensus from the 12z NAM, GFS, and Euro), then will completely engulf the state by 0z Wednesday.  The bulk of the rain will fall primarily ahead of the occluded front that the models are trying to develop , and by 12z Wednesday, the models all show the upper level low sitting atop the surface low, hinting at a decay of the surface low. The issue here is the models split the surface low into two, with the Appalachian axis serving as the bisector.  The east low appears to develop newly out of the west low, and it rapidly strengthens to precipitate heavily over SE PA, leaving room for flooding of local streams and creeks. The 540-dam line doesn't  move too much during the day, leaving the bulk of the heavy precip ahead of the surface low as rain.  

Long Term (Wednesday Night into the Weekend)

Upon nightfall, Wednesday will begin to feel the transition to a colder pattern as the weakened west low slowly moves northeast. The upper level low will remain stagnant for Wednesday and Thursday, sporadically developing isolated snow showers in and around the state. The heaviest of the snow showers will stay off to the west, but the 12z NAM spits out a stronger isolated snow cell over Harrisburg and Philly, which could lead to a burst of 3 to 4 inches of snow around these parts around 6z Thursday in a few hours (check the 4km NAM when made available) beyond this, the GFS and Euro decay the upper level low, but hint at north wind induced lake effect snow for western areas Thursday into overnight Friday, which could also be linked to a strengthening shortwave over these parts. Looking toward the weekend, the 12z Euro and GFS develop a very deep trough, and despite the GFSX MOS only dipping high temp locally into a 3 to 5 day below normal zone,  but with such low anomalous 500mb heights, look to see those MOS values drop as the week rolls along, for as of right now, the GFS implies light snow showers falling in north central Florida.