407
AWUS01 KWNH 141703
FFGMPD
NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-142302-

Mesoscale Precipitation Discussion 0685
NWS Weather Prediction Center College Park MD
102 PM EDT Mon Jul 14 2025

Areas affected...Mid-Atlantic

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

Valid 141702Z - 142302Z

SUMMARY...Convection will continue to expand across much of the
Mid-Atlantic this afternoon, resulting in scattered to numerous
instances of flash flooding. Very high rainfall rates are expected
from these storms...and some instances of significant flash flood
impacts are possible.

DISCUSSION...Latest radar and satellite imagery depicts
thunderstorms quickly developing along and near the terrain from
northeast WV into central PA. We are also seeing activity increase
in coverage farther east across PA into southeast NY. Pretty good
large scale forcing for this convection today, with a mid level
shortwave axis approaching from the west and the right entrance
region of the upper level jet overhead. Impressive thermodynamics
are also in place...with MLCAPE either currently or forecast to
get into the 1500-2500 J/KG range and PWs ranging from closer to
1.75" over central PA to near 2.1" over the eastern Mid-Atlantic.

The more organized convection will likely be the activity that is
developing on/near the terrain as of 16z. This convection should
organize as it moves east off the terrain and anticipate one or
more convective clusters to then move eastward from northern VA
into PA. This linear convection should become more progressive
with time...but will be running into an airmass with PWs
approaching 2.25", and thus even a quicker moving line will be
capable of producing very heavy rainfall amounts...possibly
upwards of 2-3" of rain in an hour.

We will also see smaller scale convective clusters develop out
ahead of this more organized line this afternoon. These storms
will likely be slower moving...generally moving off to the east
northeast around 10-15kts. These cells could also briefly
slow/backbuild into the low level flow...especially over PA into
NJ and southern NY where the low level inflow is a bit stronger
and more aligned with the deep layer mean wind. Also likely to
have some cell mergers briefly increase rainfall duration...and
around 20kts of effective shear could be just enough to briefly
sustain some multi cell structure. All this to say that these
convective clusters out ahead of the expected convective line will
also pose an increasing flash flood risk as the afternoon
progresses.

Scattered to numerous instances of flash flooding are likely
across most of the MPD area, stretching from northern VA into
southern NY. Some of this could be higher end flash
flooding...especially if/where these higher rates overlap any more
sensitive urban areas. Hourly rainfall upwards of 2-3" will be
possible in the stronger more persistent storms...with event total
rainfall likely exceeding 3" in swaths over this region. Both the
HREF and REFS also indicate a 20-40% chance of exceeding 5"
through 00z...and seeing localized totals over 5" certainly seems
plausible given the aforementioned ingredients in place.

The highest rainfall magnitudes will likely end up where we see
both merging/training convective clusters this afternoon, and the
more organized convective line(s) later this afternoon into the
evening hours. Based on HREF/REFS probabilities and current
observational trends...portions of south central to eastern PA
seem most at risk for this potential...possibly extending into
northern NJ and southeast NY as well. Farther south over MD and VA
things remain capped for now, so may have to wait until the
convection moving east off the terrain gets closer before stronger
activity initiates here.

Chenard

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

ATTN...WFO...ALY...BGM...CTP...LWX...OKX...PBZ...PHI...

ATTN...RFC...RHA...TAR...TIR...NWC...

LAT...LON   42127654 42097538 41767404 41277363 40247424
            39927456 39137602 38667721 38427911 39197911
            39467909 40157873 40997807 41837752