Technical Discussion

Synopsis:

A region of high pressure will hover over the region today, allowing for abundant sunshine.  A disturbance brewing over the Gulf of Mexico will track up the East Coast and bring the opportunity for snow to the state late Friday night through Saturday evening.  Expect mainly snow showers in northern portions of the state to mixed precipitation and even rain showers in the southernmost portions.  There will be a brief respite from the wintry weather on Sunday, with mostly cloudy skies, before another disturbance approaches by late Monday, with the potential for precipitation.

Short Term:

The models all show a nice ridge of high pressure remaining over the state today, before moving off the coast.  The models (WRF, GFS) are also quite consistent in the continuing development of an upper-level low over the Gulf of Mexico, drawing in abundant moisture.  This low is projected to track up the East Coast, with an associated surface low developing along the way.  The ensemble mean of the 2100 UTC run of the SREF precipitation/pressure projections shows the arrival of light precipitation to southern portions of the state before dawn tomorrow morning, and the precipitation progressing northward. The 1200 UTC GEFS plumes show the consistent arrival of the precipitation very early tomorrow.  There is a bit of a spread with respect to precipitation amounts, with liquid equivalents ranging from .1 - .5 inches from today into tomorrow, but the majority of the ensemble members suggest .1-.3 inches (which would correspond to approximately 1-4 inches of snow for this region).  It is interesting to note that very few members show any rain or mixed precipitation for this portion of the state (and if they do, only very briefly), but more southern regions of the state may not be able to avoid a wintry mix come tomorrow.   According to the 2100 UTC GFS & WRF runs, the 540 line is projected to cut almost directly through the state late tonight into tomorrow morning.  There is some uncertainty with respect to where the rain and snow line will fall, but current projections seem to suggest that southern regions of the state will see a mix, possibly even just changing to rain in the southernmost locations, and northern locations and the mountains will experience snowfall.  Finally, the 1500 UTC run of the SREF probability field shows increasingly high probabilities for snow over much of the state as tomorrow (Saturday) progresses, with reasonably high probabilities for freezing rain/ mix in south/southeastern Pennsylvania.  However, overall the bulk of the precipitation will remain to our southeast and off the coast.

Long Term:

Model projections show Sunday to be a relatively calm day, with mostly cloudy skies.  A new disturbance will continue to evolve over the Midwest and track eastward.  By Monday evening, a nice swath of moisture associated with the low pressure system will impact the state, bringing the opportunity for scattered snow showers.

-- Alicia Klees