Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Thu Sep 18 2025 22:38:00

AWUS01 KWNH 182237
FFGMPD
AZZ000-NVZ000-CAZ000-190436-

Mesoscale Precipitation Discussion 1103
NWS Weather Prediction Center College Park MD
637 PM EDT Thu Sep 18 2025

Areas affected...southeastern California, southern Nevada, western
Arizona

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

Valid 182236Z - 190436Z

Summary...Scattered instances of flash flooding are ongoing.=20
Locally significant impacts are possible.  The ongoing threat
should continue through at least 05Z/10p PDT.

Discussion...Scattered to numerous thunderstorm activity continues
to drift generally northward across the discussion area.  A
relatively focused cluster of storms has exhibited backbuilding
tendencies across southwestern Arizona, where a mature cold pool
has been established.  The region remains under the influence of
deep southerly flow on the eastern edge of a disturbance centered
near the California coastline south of San Luis Obispo.  The
southerly flow is maintaining a fetch of extremely moist and
unstable air from the Gulf of California, with pre-convective air
(characterized by 1000-2000 J/kg MLCAPE and 1.5-2 inch PW)
continuing to support deep moist convection.  Furthermore,
kinematics are modest enough to support slow storm  motions and
continued backbuilding - especially near mature cold pool(s) and
near terrain-favored areas.

The ongoing scenario should continue to support locally heavy
rainfall in several areas.  Local rain rates reaching 2 inches/hr
should continue.  These rates should readily exceed FFG thresholds
across the region.  Locally significant flash flood impacts remain
possible.  Over time, widespread overturning and boundary layer
cooling should result in a lessening of convective coverage, but
this process should take several hours to play out. Deep
convection is likely to be ongoing through 05Z/10p PDT.

Cook

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!9LEkFD13iGcI__47ManaCAbp6z3eXQYxs2e_668ORkWFNJ49AOANlUT_TUNIppOw6S_W=
Ny7YlvCbE6vWlrtXHe0L6rc$  for graphic product...

ATTN...WFO...FGZ...HNX...LOX...MTR...PSR...SGX...TWC...VEF...

ATTN...RFC...RSA...STR...NWC...

LAT...LON   37331872 36591507 35901209 33411127 31371148=20
            32481495 32501662 33571704 34401845 34921967=20
            36382068 37292044=20

=3D =3D =3D
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