Technical Discussion

Synopsis…

A potentially significant long-term rain event is in store for this week.

Short-term (Mon. – Wed. afternoon):

Showers are moving into Pennsylvania Sunday night, and a more steady rain is expected for the afternoon.  The models have the heaviest of this first batch of rain west of Philadelphia and Scranton but otherwise across the entire state.  The second batch of rain will have a more easterly component to its direction and affect the entire state at some point.  There is a slight chance that a few showers could linger on the backside of the system on Wednesday for Erie and Bradford, maybe as far south as Pittsburgh.  Total precip was determined using SREF plumes.

Long-term (Wed. night. – Fri.):

How strong will the second cut-off low be?  The 12Z (Sunday) and 0Z WRF indicate a strong cut-off that forms another surface low Wednesday that spreads more heavy-at-times rain across Pennsylvania Wed. night and Thursday.  The CMC shows a somewhat strong cut-off that does not form the Wed. surface low but directs the tropical system more over land.  (I assume the WRF would also show that if it went out longer.)  But the GFS has barely any cut-off low at all and pulls the tropical system off-shore.  Hence the forecasts for Thursday and Friday are as unspecific as "A chance of rain."

Longer-term:

Check out the 540 line diving through Pennsylvania during Saturday night on the GFS, with a MOS low of 39 at KUNV.  Brrrr... 

Scott Sieron