793
AWUS01 KWNH 312031
FFGMPD
NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-010100-

Mesoscale Precipitation Discussion 0836
NWS Weather Prediction Center College Park MD
430 PM EDT Thu Jul 31 2025

Areas affected...Portions of the Mid-Atlantic

Concerning...Heavy rainfall...Flash flooding likely

Valid 312030Z - 010100Z

SUMMARY...Numerous flash floods likely as multiple rounds of
storms with embedded cell mergers cause localized rainfall rates
as high as 4 inches per hour. Urban and small stream flooding
threat increasing through DC and Baltimore.

DISCUSSION...Multiple rounds of storms have developed with one
round of storms in the Shenandoah Valley, a second near the I-95
corridor from DC to Baltimore, and a third from the Delmarva
Peninsula through southern New Jersey. By far the most impressive
rainfall rates have been with the cluster in New Jersey, where
over 4.5 inches per hour rates have been noted. Fortunately for
most of the rest of the area, rates have been a bit lower,
generally between 2-3 inches per hour with the strongest storms.

The storms have been organizing into the aforementioned lines, but
their outflows and boundaries from previous storms are frequently
allowing for separate cells to develop in between the lines and
merge into them, resulting in long-duration extremely heavy
rainfall for some areas, such as in central New Jersey. Going
forward, the greatest potential for additional cell mergers and
training is across northern Virginia and central Maryland, where a
period of sunshine noted on satellite has effectively raised the
surface based instability over that area to over 2,500 J/kg, even
though some areas have already seen rain from storms earlier
today. This higher instability is supporting the storms
retrograding west to the north and west of DC and Baltimore, as
the storms follow the greatest instability. However, with the
overall movement of the storms towards the east, this has locally
supported training and prolonged duration of heavy rain near and
over those metros and their suburbs.

HiRes guidance suggests the 3 (or at least the western 2)
boundaries will eventually merge together into a cluster before
the whole complex weakens and moves east upon consuming the
aforementioned bubble of higher instability. This should finally
allow the cold front driving much of the forcing to the north to
push through the DMV and end the heavy rain and flash flooding
threat. Meanwhile further north across New Jersey, the cold front
is more progressive towards the east, so the storms should
continue to push south and east and largely end the threat from
Philly northward sooner.

Wegman

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...AKQ...CTP...LWX...PHI...

ATTN...RFC...RHA...NWC...

LAT...LON   40467440 40367411 40017412 39457441 39137460
            38937483 38447518 38377630 38347709 38167789
            38027862 38197943 38377923 38797899 39007858
            39407816 39677793 39957748 39937710 39907572
            40197501