Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Sep 27 2025 18:21:14

AWUS01 KWNH 271821
FFGMPD
AZZ000-NVZ000-CAZ000-280019-

Mesoscale Precipitation Discussion 1147
NWS Weather Prediction Center College Park MD
220 PM EDT Sat Sep 27 2025

Areas affected...southeastern California, much of Arizona, far
southern Nevada

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

Valid 271819Z - 280019Z

Summary...An increase in convective coverage is expected through
peak heating hours today.  A few instances of flash flooding are
possible.

Discussion...Recent satellite imagery depicts deepening cumulus
across a broad part of Arizona and adjacent areas of southeastern
California.  Satellite/radar also depicts a persistent, yet small
cluster of cells just north of Yuma that were producing spots of
1-2 inch/hr rain rates.  The ongoing evolution of convection is
being supported by a distinct mid/upper low centered over far
southeastern California, in addition to surface-based
destabilization due to sunshine and surface warming.  PW values
are in the 1-1.5 inch range, and SBCAPE values are around 1000
J/kg - both supporting deep convection with heavy rainfall as
cells mature.  Of note is the fact that cells closer to the
mid/upper low have been very slow to move/propagate so far due to
weak steering flow in that area.

Through the afternoon, increases in convective coverage (along
with increasing prevalence of cell mergers) are expected across
the discussion area.  A few more areas of 1-1.5 inch/hr rain rates
are expected - especially across southwestern Arizona where the
best forcing, instability, and moisture combo exists.  Isolated to
scattered instances of flash flooding are possible.  Much of the
threat should be diurnally driven and persist through 00Z/5p
PDT/6p MDT.

Cook

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!465LAeGZjIfzKRajtIB4bzB_LVQG6fPe3Wr9SHFrNOxUQnrmkE1LghNiw6JDewBiz0eo=
Bzn3zglQknUhXj5Sm59_Hmo$  for graphic product...

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

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

LAT...LON   36631405 36391160 35371041 32620945 31450974=20
            30991091 32341461 32411552 32481632 33891689=20
            34701793 36171693=20

=3D =3D =3D
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