817
AWUS01 KWNH 071550
FFGMPD
NJZ000-PAZ000-DEZ000-MDZ000-072150-

Mesoscale Precipitation Discussion 0612
NWS Weather Prediction Center College Park MD
1149 AM EDT Mon Jul 07 2025

Areas affected...Parts of the Mid-Atlantic between southern
Maryland and northern New Jersey

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

Valid 071550Z - 072150Z

SUMMARY...Slow-moving to stationary showers and thunderstorms
associated with Post-T.C. Chantal are expected to increase in
coverage and intensity this afternoon. Highly efficient tropical
downpours (2-3"/hr rates) are expected within these thunderstorms
and overlap with the urbanized corridor of eastern PA, NJ,
northern DE, and central/eastern MD. Scattered instances of flash
flooding are considered likely.

DISCUSSION...Post-T.C. Chantal was analyzed across southeast VA at
15z and continues to push northeast at around 30 mph. Meanwhile, a
surface trough extends to the northeast across the northern
Delmarva Peninsula and into northern NJ. This surface trough and
area of convergence just to the north and west of Chantal`s center
will likely become the focus for developing slow-moving
thunderstorms through this afternoon. The atmospheric environment
in place supports efficient rain processes, with PWs of 2.0-2.4"
and MLCAPE of 1000-1500 J/kg. In fact, although displaced just to
the west of the heaviest rainfall threat IAD`s 12z sounding
depicted a PW of 2.13" and freezing level of 15,788 feet, both
just below the daily max.

There is anticipated to be two separate modes of heavy rainfall
along the highlighted area from southern MD to northern NJ through
about 21z. The first area of concern is near the center of
Post-T.C. Chantal as it crosses over the Delmarva. Here,
slow-moving thunderstorms will feed off enhanced tropical moisture
(PWs over 2.3") and elevated levels of effective bulk shear (over
25 kts). Additionally, as the center of Chantal opens into more of
a mid-level trough by later this afternoon, weak steering flow
will be evident directly under this trough across the Delmarva.
This region is where the greatest potential exists for rainfall
rates to reach or even briefly exceed 3"/hr, as well as rainfall
totals exceed 5" potentially. The other area of concern will be
across eastern PA and NJ where mean layer flow of 20 kts out of
the south-southeast and out of an area of greater instability
(greater than 3000 J/kg of SBCAPE) will promote back-building or
stalled thunderstorms within a moist environment. Here, impacts
are expected to remain mostly localized as storms remain generally
small in size, but some impacts could be considerable given the
urban and sensitive terrain.

This region is most likely to experience impacts associated with
urban flooding or rapid ponding of water on roadways, with an
exception in southeast PA and central NJ where more rural and
suburban flash flooding is possible near rivers and streams given
the sensitive terrain and 1-hr FFG less than 1.5-2.0" in spots.

Snell

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

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

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

LAT...LON   40877524 40677446 39917465 38557534 38087589
            38227669 39197671 40287619