Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Mon Aug 25 2025 21:46:36

AWUS01 KWNH 252146
FFGMPD
AZZ000-CAZ000-260145-

Mesoscale Precipitation Discussion 1003
NWS Weather Prediction Center College Park MD
545 PM EDT Mon Aug 25 2025

Areas affected...Southern CA...Southwest to South-Central AZ

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

Valid 252145Z - 260145Z

SUMMARY...Locally very heavy monsoon-driven showers and
thunderstorms are expected going through the remainder of the
afternoon across southern CA into southwest and south-central AZ.
Scattered areas of flash flooding are likely, some of which may be
locally significant.

DISCUSSION...The mid-afternoon GOES-W VIS/IR satellite imagery
shows deepening and cooling convective tops across southeast CA
and into adjacent areas of southern AZ where radar is confirming
multiple concentrated bands of very heavy shower and thunderstorm
activity.

Mesoscale boundary forcings/interactions along with terrain
influence and proximity of a very moist and unstable airmass is
expected to drive corridors of additional convection with high
rainfall rates going into the evening hours. MLCAPE values of 1500
to 2500 J/kg are noted with recent CIN erosion helping to yield
the recent uptick and organization of convection across southern
CA and southern AZ. This includes the Peninsular Range and the
adjacent deserts off to the east and south.

Given the level of focused instability over the region with PWs
reaching nearly 2.5 standard deviations above normal (with support
from the very warm nearby Gulf of California), some rainfall rates
may reach 2 to 2.5 inches/hour, with some spotty storm totals over
the next few hours of 3 to 4+ inches. Recent WoFS guidance output
suggests this potential, which will be aided by some localized
cell-merger activity.

Additional areas of flash flooding will be likely, some of which
may be locally significant near areas of higher terrain and also
for the dry wash/arroyo locations near and away from active areas
of heavy shower and thunderstorm activity.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!7vkAaj75rcrt-PIafMfdv1fVW3ZEAJXG763nWXhF9O2-b5Z22oJsCgvTPWRZV_AGO3EW=
JGgmSXtpxO1OjwL-sJcN_vA$  for graphic product...

ATTN...WFO...PSR...SGX...TWC...VEF...

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

LAT...LON   34681677 34481604 33611488 33431359 33201277=20
            33111094 32761015 31791014 31241072 31481240=20
            32001378 32321480 32411608 32861673 33841716=20
            34521716=20

=3D =3D =3D
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