Technical Discussion

Synopsis:

A trough of low pressure will hover over the state through the mid-week, allowing for unsettled conditions.  The passage of a cold front Monday into Tuesday will bring precipitation off and on from late tonight through late Wednesday.  Later in the week, high pressure will manage to gain control, so expect drier and sunnier conditions.

Short-Term:

The 1200 UTC runs of both GFS and WRF are projecting a trough anchored over much of the United States to dominate the weather through Wednesday.  A surface low pressure system is forecasted to pass through Pennsylvania, dropping a cold front through the state late Monday into Tuesday.  All models are projecting precipitation in association with this front.  The 1500 UTC run of the SREF plumes suggests a round of precipitation starting late tonight and lasting through Wednesday, with perhaps a small respite on Tuesday.  For State College, the bulk of the ensemble members are forecasting below .4 inch total precipitation.  For Philadelphia, the bulk of the ensemble members are projecting even lower amounts.  This does not seem like a significant precipitation event for the bulk of the state through Tuesday, although northwestern and western portions of the state could see up to 1.6 inches of precipitation when all is said and done, according to the SREF runs. 

Long-Term:

The 1200 UTC runs of SREF precipitation type probabilities and the 850 mb temperature projections in general all suggest the precipitation to be purely rain through Tuesday.  However, with the cold air advection building in after the passage of the cold front by Wednesday, snow showers and mixed precipitation could be likely in higher elevations and northwestern portions of the state.  We forecasted accordingly and carefully.  The 1200 UTC runs of MOS temperature projections show the low temperatures Wednesdaynight barely breaking freezing as well. The 1200 UTC runs of both WRF and GFS show a ridge of high pressure dominating by Thursday, allowing for mostly sunny skies, as dry conditions are projected for all levels of the atmosphere.