Weather Prediction Center issues Mesoscale Precipitation Discussion #776 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE940
AWUS01 KWNH 190038
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MAZ000-RIZ000-CTZ000-NYZ000-190600-
Mesoscale Precipitation Discussion 0776
NWS Weather Prediction Center College Park MD
837 PM EDT Sat Jul 18 2026
Areas affected...Southern New England & Long Island...
Concerning...Heavy rainfall...Flash flooding possible
Valid 190040Z - 190600Z
SUMMARY...Over-running showers/thunderstorms aligning for
increasing training potential of moderate to occasionally heavy
rainfall (rates 1.5-2"/hr). Localized 2-3.5" totals may result in
scattered flash flooding potential through early overnight period.
DISCUSSION...00z surface analysis shows warm front is slowly
progressing through the Hudson River Valley but bends due east
parallel to the southern coast of Long Island. However,
southeasterly flow from the warm conveyor belt off the
Mid-Atlantic Coastal region with well above average low level
moisture (surface Tds to mid-70s) is confluent with low to
mid-level flow streaming out of the Ohio Valley and through
Allegheny Plateau into southern New England. High theta-E air
just above the surface through isentropic ascent and steepening
lapse rates further aloft (600-400mb) provide ample 2000+ J/kg
MUCAPE. Given confluence of the streams there is solid mass
convergence along/north of the front for slightly elevated
convective development over the last few hours. As cold front
approaches from the northwest along with upper-level height-falls
should continue to support moisture flux convergence along the
north-south oriented warm front for upstream redevelopment as
well.
Given total PWats of 2-2.5" should allow for efficient rainfall
production, combined with smoke helping raindrop nucleation with
more numerous smaller rain-drops for collision/coalescence
processes may increase rainfall efficiency toward 2"/hr. Given
deep layer steering above 700mb is also allowing for
repeating/training elements across S CT, RI and Long Island; there
is potential for localized 2-3.5" rainfall totals. This is in the
range of the 1 to 3 hour FFG values (2-2.5" and 2-4",
respectfully) suggesting scattered incident or two of flash
flooding will remain possible. This only increases within
hydrophobic urban environments.
Gallina
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...ALY...BOX...OKX...
ATTN...RFC...TAR...NWC...
LAT...LON 42167286 42157142 42027005 41676988 41216992
41167066 40887203 40657332 41097383 41497411
41997413
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #776 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE----------------
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