996
AWUS01 KWNH 301540
FFGMPD
PAZ000-MDZ000-VAZ000-WVZ000-302000-

Mesoscale Precipitation Discussion 0557
NWS Weather Prediction Center College Park MD
1139 AM EDT Mon Jun 30 2025

Areas affected...Portions of the Central Appalachians in PA, MD,
WV, and VA

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

Valid 301538Z - 302000Z

Summary...Thunderstorms should develop between Noon and 2 PM EDT
in the Allegheny Mountains, Blue Ridge Mountains, southwest
Pennsylvania, and surrounding areas. The storms may initially move
slowly to the northeast, and the slow movement and heavy rain
rates, with over 1 inch of rainfall in an hour, may lead to
localized flash flooding in the early afternoon.

Discussion...Thunderstorms will become more numerous over the next
couple hours in the central Appalachians as most locations reach
the convective temperature in the low 80s, as indicated in the 12Z
PBZ and RNK soundings. Initiation will be favored first near the
ridge lines, and this is already evident in visible satellite
trends. LightningCast suggests that some lightning, and thus more
vigorous convective rainfall, may begin by 1630Z in at least a few
areas of the Allegheny and Blue Ridge Mountains. For the first
couple hours, convection is likely to move slowly to the northeast
based on hi-res model reflectivity and deep layer mean wind around
10-15 knots. In some cases, this may lead to some training
patterns where the terrain is closer to parallel with the mean
wind vector. But slow storm motion could sustain heavy rain rates
long enough over individual locations in general, and that could
lead to some localized flash flooding.

The probable increase in flash flood threat in the next few hours
is supported by the latest 12Z HREF probabilities showing
increasing chances of 1 inch per hour rain rates and 1hr and 3hr
FFG exceedance in these areas between 17Z and 20Z. The environment
is very supportive of intense instantaneous rain rates with
precipitable water values generally above the 95th percentile for
late June through the depth of the column (based on overall PW
percentiles and CIRA layer PW products). Therefore, it would be
plausible to even see some locations exceed an inch of rain in 30
minutes in the strongest convection.

Much of this area will be upgraded to a Slight Risk on the 16Z Day
1 ERO, which will be issued shortly.

Lamers

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

ATTN...WFO...CTP...LWX...PBZ...RLX...RNK...

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

LAT...LON   41237901 40897858 40647797 39587776 38587806
            37987901 37237984 37578103 38398081 39497985
            39937999 40318031 40858008 41197955