Technical Discussion

Synopsis:

A cut-off low will hover over or near the state, bringing the opportunity for showers, especially in western regions of the state through Tuesday.  A high pressure system will push the low off the coast, allowing for drying conditions and lots of sunshine on Wednesday and Thursday.

Short-Term:

Tonight, we forecasted the continuing chance of precipitation, albeit scattered showers.  The 900 UTC runs of the SREF probability fields shows a very low, but non-zero, probability of snow or other mixed precipitation types for the ridges in west-central Pennsylvania.  We were sure to not go overly dramatic with this, though.   The rain probability is quite high, especially for the western half of the state throughout tonight.  The 1200 UTC run of WRF supports the scattered showers tonight.  Tomorrow, the 1200 UTC runs of both the WRF and GFS show the cut-off low just starting to move out of Pennsylvania, still allowing for spotty showers.

Long-Term:

The 1200 UTC runs of WRF and GFS have consistency in projecting spotty precipitation to taper off by Tuesday, except perhaps in the most eastern portions of the state.  The 1500 UTC run of the SREF plumes suggest precipitation ending by Tuesday.  There is a wide ensemble spread, but the mean is around .2-.3 inches of rain by Tuesday for the State College, so this is clearly not an overly significant precipitation event here.  Further west, though, for example in the run for the Pittsburgh area, rain totals are projected between .5 and .9 inches.  The 1200 UTC run of the GEFS plumes shows a similar duration of the precipitation event, but is forecasting slightly lower totals.  After the cut-off low finally moves off the coast, all model guidance suggests that high pressure will build into the region, with the relative humidity plots showing a drying atmosphere at all levels.