Mesoscale Precipitation Discussion 0265
NWS Weather Prediction Center College Park MD
343 PM EDT Tue May 13 2025

Areas affected...South-central PA...Western MD...Eastern WV...Far
Northwest VA...

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

Valid 131945Z - 140100Z

SUMMARY...Continued moderate rainfall with occasional weak
embedded convective elements within strong orthogonal upslope
ascent regime.  Localized spots of additional 1.5-2.5" totals
possible within broader .5-1" average by early overnight.

DISCUSSION...A strong moist dynamic environment across the
Allegheny section of the larger Allegheny Plateau in far NE WV, W
MD into south-central PA is expected to persist through the
evening with a very slow south to north advancement along the
ridge lines. Highly anomalous warm conveyor belt with nearly all
CIRA LPW layers at or above the 95th percentiles with maxima at
the lowest sfc-850. Combine this with persistent, nearly
orthogonal 35-40kts of 925-700mb winds per VWP is resulting in IVT
values over 600-700 kg/m/s even without support of increased
vertical potential from insolation.  As a result localized totals
have already been over 2-4" throughout the day in E WV/W MD and
starting to reach 2-3" across Somerset county in PA.  Slightly
lower vertical exposure across the Blue Ridge, still spots of
1.5-2.5" have been observed.  Additional rainfall will compound
and expand ongoing flooding concerns through the complex terrain
through 00z.

GOES-E WV suite shows broad closed low across the Ohio Valley,
though an eastward extension of the low/vorticity maxima is
lifting across SW VA/S WV at this time, surface winds are backing
in response to the height-falls and the 850mb trof is sharpening
increasing directional convergence from more westerly return flow
intersecting the 30-40kt WCB flow.  Additionally, best diffluent
region of the upper-level jet is starting to lift northward ahead
of the 850mb trof with apex of the split along the Allegheny ridge
as noted in the broad cirrus shield (starting to evacuate Northern
VA/E WV.  While there will be some insolation, the timing is
likely limited across and north of I-64; with strong instability
gradient noted in RAP analysis.  Still, with the DPVA approaching
and some temps rebounding into the low to mid-70s, modified
sounding across central VA would support 500-1000 J/kg of MLCAPE
that could be utilized in further ascent on the 850mb convergence
line.  Upstream convection along Albemarle/Augusta can be seen
developing in this instability axis and with 700-500mb flow veered
a bit, the cells should track NNW into the most affected areas
with localized enhancements to the WCB moisture flux to support
.5-1"/hr rates for embedded convective elements through the
complex terrain.

Rapid refresh guidance (HRRR/RRFS/WoFS) are inconsistent in
placement, as expected, but continues to support those embedded
additional 1.5-2.5" totals within a broader field of .5-1" totals,
likely to maintain on going flooding, slowly expanding coverage
northward of flooding risk through the early overnight period.

Gallina

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

ATTN...RFC...MARFC...OHRFC...NWC...

LAT...LON   41277830 41187740 40827691 40267683 38947785
            38107867 38167922 38757974 39667966 40617905