Weather Prediction Center issues Mesoscale Precipitation Discussion #1136 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE083
AWUS01 KWNH 251856
FFGMPD
MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-NJZ000-PAZ000-260050-
Mesoscale Precipitation Discussion 1136
NWS Weather Prediction Center College Park MD
255 PM EDT Thu Sep 25 2025
Areas affected...northern Mid-Atlantic into southern New England
Concerning...Heavy rainfall...Flash flooding possible
Valid 251854Z - 260050Z
Summary...Training axes of heavy rain are expected from the
northern Mid-Atlantic region into southern New England through the
late afternoon and evening. Hourly rainfall of 1 to 2+ inches may
result in localized flash flooding with a focus on any urban
centers.
Discussion...Radar imagery at 1845Z helped identify a pair of MCVs
over the Northeast, embedded within areas of largely stratiform
rain from portions of PA into New England. One vortex over central
PA and the other near Albany, NY, were tied to surges of higher
rainfall rates, with MRMS-derived values between 1 and 2 inches in
an hour at times. These two features were located along the
northern edges of a region of elevated CAPE with 500-1500 MUCAPE
identified on 18Z SPC mesoanalysis data. The environment was
characterized by anomalous moisture with PW values of roughly 1.7
to 2.0 inches (2 to 3 standardized anomalies above the mean for
late September), supportive of hourly rainfall locally in excess
of 2 inches.
As a cold front over central NY/PA and the aforementioned
mesoscale waves continue to advance downstream, interaction with
500-1000 J/kg MLCAPE from southeastern PA into far southern New
England will support an increase in rainfall coverage and rates
from the northern Mid-Atlantic into southern New England. Some
breaks in cloud cover noted on visible imagery over southeastern
PA into NJ may help to locally increase instability through better
surface heating, yielding greater potential for higher intensity
rainfall. While individual cell motions should remain progressive
toward the NE, alignment of convective axes with the southwesterly
deep-layered steering flow will promote training and locally 1 to
2+ inches of rain in an hour at times. These locally higher rates
could result in a relatively quick accumulation of rainfall
totaling 2 to 3+ inches through 01Z. Localized flash flooding may
occur as a result, especially if overlap occurs with impervious
urban areas.
Otto
...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 44247137 43667053 43137030 42647034 42237087
41847183 41297270 40817343 40227422 39927557
39917773 40897709 42027600 42747491 43117379
43807248
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #1136 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE----------------
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