Mesoscale Precipitation Discussion 0532
NWS Weather Prediction Center College Park MD
434 PM EDT Fri Jun 27 2025

Areas affected...Central to Southern Appalachians

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

Valid 272033Z - 280230Z

Summary...Scattered pulse thunderstorms will develop through the
evening across the Central and Southern Appalachians. Rainfall
rates may briefly reach 3"/hr, producing short duration rainfall
of 1-2". This could result in instances of flash flooding.

Discussion...The GOES-E visible imagery this afternoon shows
widespread convective development across the Appalachians. In
general, these cells are discrete and scattered in a weakly forced
environment, but local enhancement due to terrain features or
storm mergers/outflow collisions have resulted in scattered
clusters across the region as well. Thermodynamics today are
favorable for heavy rainfall as PWs of 1.5 to 1.75 inches are
collocated with SBCAPE of 2000-3000 J/kg. Forcing for ascent is
generally provided via low-level upslope flow into the terrain and
surface convergence along mergers/collisions, but weak diffluence
aloft is also providing modest ascent in the area. Together, this
ascent working into the favorable environment has produced
radar-estimated rain rates of 1.5 to 2 inches per hour.

The CAMs are in generally good agreement that scattered
thunderstorms will continue to develop and move chaotically
through loss of instability or convective overturning this
evening. Mean 0-6km winds of just 5-10 kts combined with minimal
bulk shear will provide a setup that supports primarily pulse
convection with limited temporal duration. However, both the HREF
and REFS ensembles indicate a moderate to high chance (50-70%) of
at least 1"/hr rates leading to short-term rainfall as much as
1-2", and 15-min rainfall from the HRRR as much as 0.75" (brief
3"/hr rates). With storms expected to just drift across the area,
any storm that occurs atop sensitive terrain or more urban areas
could result in instances of flash flooding.

While the threat is expected to be generally isolated, there is
some potential in the next few hours of a more focused area of
convection in KY and eastern TN. Here, pulse storms developing to
the east will drift NW (along with outflows) and potentially merge
with clusters coming out of the west. Some merging of these cells
is shown, albeit with a lot of spatial spread, on the HRRR,
NAM3km, and RRFS, which could briefly enhance the convection and
accompanying heavy rainfall rate. Should this occur over some of
the more sensitive soils (FFG as low as 1.5-2"/3hrs) it could
cause a slightly higher risk for instances of flash flooding than
the more isolated pulse type storms forecast across most of the
area.


Weiss

ATTN...WFO...FFC...GSP...ILN...JKL...LMK...MRX...OHX...RLX...
RNK...

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

LAT...LON   38768309 38568231 38268169 38058093 37368059
            36588093 35798137 35338181 34908248 34538358
            34528441 34818500 35458507 37038477 38368414