Mesoscale Precipitation Discussion 0652
NWS Weather Prediction Center College Park MD
1215 PM EDT Thu Jul 09 2026

Areas affected...Central Appalachians through the Mid-Atlantic

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

Valid 091613Z - 092200Z

Summary...Showers and thunderstorms will rapidly increase in
coverage this afternoon across the Mid-Atlantic. Rainfall rates of
2-3"/hr are likely at times, leading to 2-4" of rain with locally
higher amounts. Flash flooding is possible.

Discussion...The GOES-E Experimental Day-Cloud Phase RGB this
morning features rapidly expanding coverage of Cu/TCu reflected by
glaciation development within deeper cloud structures. This is
occurring primarily within cloud breaks in the visible satellite
imagery, and is leading to a quick uptick of elevated reflectivity
with showers and thunderstorms spreading from eastern KY through
southern PA.

Forcing for ascent is steadily intensifying across the
Mid-Atlantic, leading to a concurrent increase in the flash flood
risk. A shortwave noted in WV imagery is lifting E/NE out of KY,
working in tandem with the RRQ of a modest jet streak aloft to
produce synoptic ascent. At the same time, modest 850mb inflow of
10-15 kts (locally accelerated in the vicinity of the northeast
advancing shortwave) is isentropically ascending a stationary
front to produce additional lift. Together, this overlapped ascent
is acting upon robust thermodynamics reflected by PWs measured via
the 12Z soundings that are above previous daily records (2.17" at
IAD) and a ribbon of MLCAPE already reaching 1000+ J/kg (2000 J/kg
within clearing sky conditions). Despite convection being fresh,
MRMS hourly rainfall has been above 1 inch in some areas,
indicative of the impressive environment in place.

Convection should continue to rapidly expand and intensify during
the next few hours as the shortwave lifts northeast. The high-res
CAMs, although a bit slow to develop the ongoing activity, are in
good agreement that thunderstorms will develop along any
boundaries (terrain, differential heating, outflows) and become
numerous with at least modest organization into clusters likely
through bulk shear of 25-35 kts. This will intensify rain rates
even further, and both the HREF and REFS depict a 30-40% chance of
at least 2"/hr rates this aftn, with short-term rates of 3-4"/hr
possible as reflected by the sub-hourly HRRR. The regional
soundings and forecast 0-6km mean winds suggest storms will
generally move steadily E/NE, but short-term training is likely as
Corfidi vectors align parallel to the mean flow and storms
repeatedly develop back into the higher instability.

This region is naturally vulnerable to intense rain rates both due
to sensitive terrain as well as urban areas. Additionally, 7-day
rainfall that has been 400% of normal has led to 0-10cm RSM of
60-70% according to NASA SPoRT. This suggests the region has
become even more compromised, so any repeating of these intense
rain rates could cause flash flood impacts through the aftn.


Weiss

ATTN...WFO...AKQ...BGM...CTP...LWX...OKX...PBZ...PHI...RLX...
RNK...

ATTN...RFC...RHA...TAR...TIR...NWC...

LAT...LON   41047622 41027511 40827395 40157384 39237458
            38517578 38137745 38007867 38058006 38488095
            39088145 39828135 40408045 40867806