762
AWUS01 KWNH 141557
FFGMPD
PAZ000-MDZ000-VAZ000-NCZ000-WVZ000-142100-

Mesoscale Precipitation Discussion 0268
NWS Weather Prediction Center College Park MD
1157 AM EDT Wed May 14 2025

Areas affected...Central Appalachians

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

Valid 141556Z - 142100Z

Summary...Showers and thunderstorms will expand in coverage and
intensify through the afternoon across the Central Appalachians.
Rainfall rates of 1-2"/hr are expected, which could result in 2-3"
of rain in a few areas. This rain atop saturated soils could cause
instances of flash flooding.

Discussion...The GOES-E Day-Cloud distinction RGB imagery late
this morning indicates fresh updrafts beginning to expand across
northern NC and into parts of southern VA. These updrafts are
resulting in intensifying showers and isolated thunderstorms noted
via the regional radar mosaic, and are occurring in a region of
expanding lightning cast probabilities above 30%. This suggests
that destabilization is rapidly occurring, which is reflected by
the SPC RAP analysis showing that CIN has eroded and SBCAPE has
climbed to as high as 1000 J/kg. Within this environment, forcing
for ascent is increasing downstream of a potent shortwave, clearly
noted in WV imagery, lifting northward within a synoptic trough
oriented NW to SE across the region. Downstream of this trough
axis, winds veer through the column which is helping to both
transport higher moisture northward (PWs measured around 1.2
inches which is close to the 90th percentile for the date) and
force orographic lift as sfc-925mb winds lift out of the SE,
leading to an even more impressive overlap of thermodynamics and
ascent by this aftn.

The high-res CAMs are in good agreement that clusters of
thunderstorms will continue to develop and move slowly northward
on 0-6km mean winds of around 10 kts. These storms will likely
intensify through the aftn as SBCAPE reaches as high as 1500 J/kg,
which will be acted upon by the approaching shortwave and
continued orographic/upslope low-level ascent. This favorable
environment will support rainfall rates for which both the 12Z
HREF and 00Z REFS indicate have a 40%-50% probability for
exceeding 1"/hr, with the HRRR suggesting a threat for more than
0.5"/15min at times (>2"/hr rates). Although bulk shear will
remain weak at 20 kts or less, some repeating clusters of storms
are possible, lengthening the duration of heavy rain which could
lead to pockets of event-total rainfall reaching 2-3" in some
areas.

Although convection will generally remain scattered outside of
small clusters, flash flooding will be a concern beneath any heavy
rain producing cells today. This is due primarily to these
excessive rain rates moving across extremely saturated soils from
24-hr rainfall as much as 3-6". This has compromised FFG to as low
as 0.5" to 1" in 3 hours, for which the HREF and REFS both
forecast a 50-60% chance of exceedance, highest from the Blue
Ridge of VA northward into the Potomac Highlands and Allegheny
Mountains.

Weiss

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

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

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC...

LAT...LON   40277930 40047856 39297808 38207806 37227848
            36747909 36357980 36308022 36398097 36758134
            37578125 38808083 39778047