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AWUS01 KWNH 091616

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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



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



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

RNK...



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



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