Mesoscale Precipitation Discussion 0538
NWS Weather Prediction Center College Park MD
230 AM EDT Wed Jul 25 2018

Areas affected...East-Central PA

Concerning...Heavy rainfall...Flash flooding possible

Valid 250630Z - 251230Z

Summary...Heavy rainfall should slowly decline in intensity over
the next several hours across central PA.  Hourly rain totals to
1" initially, with local amounts to 2" are expected through 12z.

Discussion...Showers and thunderstorms with heavy rain have formed
a band across east-central PA into the Southern Tier of NY over an
area of saturating soils.  Precipitable water values of 2-2.25"
lie in the area per GPS values at the periphery of the region. 
Inflow at 850 hPa is convergent out of the south to
south-southwest at 20-40 kts per VAD wind profiles, which is
importing ML CAPE values of 500+ J/kg into the region.  CIN
remains minimal.  Effective bulk shear values of ~30 kts combined
with nearly unidirectional flow out of the south have helped
organize the band.

Initially, hourly rain totals near or above 1" are expected.  With
instability slowly eroding, believe hourly rain totals will begin
to come downward with time, transitioning this into more of a
longer duration rain event.  The 00z HREF probabilities of 0.5"+
an hour slowly fade with time across the area for this reason. Of
some concern is a broken band of showers and thunderstorms within
an area of greater instability across western PA which may move
into the region from the west and reinforce -- or take the place
of -- the band later this morning as the winds at 850 hPa veer
more southwesterly.  The mesoscale guidance agrees on local
amounts to ~2" through 12z which appears reasonable. 

Roth

ATTN...WFO...BGM...BUF...CTP...LWX...PHI...

ATTN...RFC...MARFC...NERFC...OHRFC...

LAT...LON   42687589 41807578 39927664 39697700 39677770
            40227808 40997817 41507817 42007804 42477757
            42607673