Mesoscale Precipitation Discussion 0474
NWS Weather Prediction Center College Park MD
629 PM EDT Tue Jun 17 2025

Areas affected...Western/Central PA...Western/Central
MD...DC...Southeast OH...WV...Western VA...Eastern KY...

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

Valid 172230Z - 180430Z

SUMMARY...Slow moving clusters of intense deep warm cloud rainfall
production across saturated and steep terrain likely to see
additional flash flooding incidents through early overnight
period.

DISCUSSION...22z surface analysis shows a slowing of the eastward
advancement of the warm front across the Allegheny Plateau in
Northern PA but better erosion of the low level stratus across
central MD into south-central PA.  However, with weak surface wave
pressing east of the Appalachian Continental Divide, surface to
boundary layer winds have increases along front int MD and
northern VA resulting in dual moisture flux stream into the
eastern portion of MPD area.  Strong cluster near Fulton county,
PA is likely to slow with the forward advancement of the front,
but with solid upstream moisture flux streaming out of the Ohio
Valley and then eastward, continued back-building upstream
redevelopment environment will further expand the potential for
intense rainfall.  Total PWats over 2" are analyzed though both
lower elevations but even with losing some vertical depth, values
over 1.75" across much of the area of concern with maintained
20-25kts of inflow and sufficient surface theta-E to keep
saturated mid-level lapse rates still unstable with narrow skinny
CAPE profiles should result in continued very efficient rainfall
production with 2"/hr rates in the strongest cores. 

Aloft, solid right entrance divergence into 50-60kt jet over NY
into New England will likely keep upslope strong though also
support greater forward propagation of cells across SE OH, WV into
W PA, but streaks of quick 1.5-2" in the rugged terrain is likely
to result in localized flash flooding through the overnight. 
However, there is a sharpening SW to NE line of mid-level
suppression north of the jet axis currently seen from just off
Lake Erie in NE OH back toward NW OH/central IND.  This is
pressing southeastward with northern stream height-falls...and
will likely further corral warm-cloud showers for better repeating
potential across SE OH/WV as well.  Recent Hi-Res CAMs including
HRRR, RRFS and 19,20,21z WoFS strongly suggest best potential
remains across SW to south-central PA with even some higher
probabilities of locally exceeding an additional 3" inches in
places.  This may result in a possible incident or two of
significant/considerable flash flooding, within the broader area
of scattered likely flash flooding incidents.

Gallina

ATTN...WFO...CTP...JKL...LWX...MRX...PBZ...PHI...RLX...RNK...

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

LAT...LON   41627873 41417706 40837614 40227577 39747597
            39127655 38557764 38167860 37487991 37338024
            36818188 36688288 36748415 37258437 38388288
            38718261 39238223 40668093 40898047 41517953