Weather Prediction Center issues Mesoscale Precipitation Discussion #927 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE734
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Mesoscale Precipitation Discussion 0927
NWS Weather Prediction Center College Park MD
208 PM EDT Wed Aug 13 2025
Areas affected...Northeast PA...Northern NJ...Southeast
NY...Southern New England
Concerning...Heavy rainfall...Flash flooding possible
Valid 131808Z - 140000Z
SUMMARY...Increasing coverage of heavy showers and thunderstorms
may produce isolated to scattered areas of flash flooding going
through early this evening.
DISCUSSION...The early afternoon GOES-E visible satellite imagery
along with radar shows a gradual expansion of shower and
thunderstorm activity occurring across areas of northeast PA and
southeast NY. This convection is forming within an increasingly
moist and unstable airmass that is currently characterized by
MLCAPE values of 1000 to 2000 J/kg and PWs of generally near 1.75
inches.
Meanwhile, there is some upper-level support with the approach of
an upstream vort center over northern PA which coupled with
localized orographics and additional diurnal heating should favor
additional expansion of heavy shower and thunderstorm activity
over the next several hours which will include areas farther east
eventually inclusive of northern NJ, the northwest suburbs of New
York City, and adjacent areas of southern New England.
Rainfall rates with the stronger storms will be capable of
reaching 1.5 to 2.5 inches/hour, and with slow cell-motions and
some concerns for localized backbuilding and training of
convective cells, some rainfall totals by this evening may reach 3
to 4+ inches. This is generally supported by the 12Z HREF guidance.
The antecedent conditions across much of the region are on the dry
side, and this will mitigate the flash flood threat to an extent.
However, with such high rainfall rate potential and the localized
storm totals that may occur, there may be some isolated to
scattered flash flooding concerns. This will especially be the
case near areas of more rugged terrain such as the Poconos and
Catskills, along with any of the more urbanized locations to the
northwest of New York City and across southern New England.
Orrison
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...ALY...BGM...BOX...BTV...CTP...GYX...OKX...PHI...
ATTN...RFC...RHA...TAR...NWC...
LAT...LON 43657338 43497218 42507219 41807271 41257366
40897475 41037599 41497634 41827601 42297536
42907444
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #927 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE----------------
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