Technical Discussion

Synopsis….

An approaching low pressure system from the southwest will bring moderate to heavy rainfall to the state Monday into Tuesday.  An associated sharp cold front will move through the state on Tuesday, creating conditions favorable for an isolated thunderstorm or two along with the rain showers in parts of the state.   High pressure will build into the region on Wednesday, allowing for drier and seasonable conditions to set in for the remainder of the week.

Short Term….

Generally, the models in the SREF ensemble (9 UTC run) were in decent consensus on the arrival of the precipitation to the southern portions of the state by Monday morning, although a few models were a little bit behind.  The models seem to be projecting the most significant precipitation heading into the state Monday into Tuesday.  This is also shown in the SREF plumes, which, as an example, for State College have anywhere from .2 to .4 inches 3 hour precipitation totals projected Monday into later Tuesday, with the average around up to .2 inches.  The 1200 UTC run of the WRF has most of the precipitation clearing out by very early Wednesday morning, which is supported by the SREF plumes as well.  We were not hesitant in predicting moderate to even heavy rainfall for the majority of the state during this time period due to the aforementioned evidence.  We were very conservative, though, in mentioning the chance of an isolated thunderstorm or two on Tuesday in association with the passage of the cold front, due to the less than impressive MUCAPE plumes value for much of the state, except perhaps the south-eastern portions.

Long Term….

There was not much uncertainly in the long-term forecast, due to the high pressure settling into the region after the low pressure system and cold front move off to our north-east.   Few issues were had with temperature projections after the passage of the cold front—we projected around seasonable temperatures.  It was evident on numerous models (WRF, GFS, etc.) that there will be dry air over the region as well at least later Wednesday into Thursday in association with this high pressure.