AWUS01 KWNH 181108
FFGMPD
NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-181706-

Mesoscale Precipitation Discussion 0762
NWS Weather Prediction Center College Park MD
707 AM EDT Sat Jul 18 2026

Areas affected...portions of the Mid-Atlantic States

Concerning...Heavy rainfall...Flash flooding possible

Valid 181106Z - 181706Z

Summary...Showers and thunderstorms are showing increasing
rainfall efficiency across southwest PA and have been efficient
near the Chesapeake. Hourly rain amounts to 2.5" could lead to
flash flooding.

Discussion...A shortwave moving across OH is leading to increasing
difluence aloft. To its east, showers and thunderstorms have
shown some backbuilding/short periods of training in southwest PA
and near Chesapeake Bay near a thermal gradient and within a
region of 850 hPa confluence. Precipitable water values are
1.5-2" per GPS data. Effective bulk shear is close to 25 kts,
which is leading to occasional convective organization. MU CAPE
in the region is 1000-2000 J/kg.

The mesoscale guidance has a poor handling of the PA activity, and
no handling of the activity near Chesapeake Bay. The available
ingredients support hourly rain amounts to 2.5". The 06z
GFS-based GDI supports the ongoing activity in southwest PA and
implies broadening convective coverage with time across portions
of the Mid-Atlantic States generally south of the mesoscale
guidance signal. This appears aligned with forward propagating
convective vectors, which point east to east-southeast. Daytime
heating should lead to a reduction of CIN/increase in ML CAPE
whose gradient should shift north with time, but the degree of
convection across the area will dictate how quickly the
instability gradient/effective front lifts northward. Confidence
is lower than average in the specifics, but flash flooding would
be possible, particularly in urban areas.

Roth

ATTN...WFO...AKQ...CTP...LWX...OKX...PBZ...PHI...

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

LAT...LON 40977758 40827554 40697435 40317387 39617398
38737466 38647630 39317844 40147999 40917996

$$

--- Scorpio BBS
* Origin: capitolcityonlinet.net * KY, USA (618:250/10)