Technical Discussion

Synopsis: 

High pressure will hover over the Commonwealth through Tuesday, allowing for mostly sunny skies and dry conditions.  A low pressure system will approach the region later in the week, dropping a cold front through the state Wednesday night through Thursday.   The disturbance will bring the opportunity for scattered showers late Wednesday into Thursday.

Short-Term:

The 1200 UTC runs of both WRF and GFS project the surface high pressure system to continuing dominating the weather through Tuesday.  The relative humidity plots show a dry slot over the state through mid-Wednesday when the moisture swath approaches.  Accordingly, we forecasted mostly sunny skies and fair conditions through early Wednesday, nothing tricky in the forecast.

Long-Term:

The 1200 UTC runs of the GEFS plumes show precipitation beginning late Wednesday evening.  The bulk of the ensemble members are consistent in projecting only .1 - .2 inches of precipitation for State College when all is said and done and under .25 inches for Harrisburg, for example.  However, most of the GEFS ensemble members are forecasting a switch to snow as Thursday progresses, which we thought was a tad shady, given the projected 850 mb temperatures and such.  The 1200 UTC runs of SREF are projecting similarly low amounts of precipitation on Wednesday into Thursday, although the SREF does not indicate any snow or mixed precipitation.  The 1200 UTC run of the CMC supports precipitation beginning late Wednesday evening and lasting through late Thursday.  We forecasting accordingly, with scattered showers late Wednesday through late Thursday.  Finally, the 1200 UTC run of GFS suggests nice cold air advection, illustrated by reasonable solenoids, when the low pressure system moves to our east on Thursday; we took this into account when forecasting temperatures.