Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Aug 23 2025 22:37:07

AWUS01 KWNH 232237
FFGMPD
NVZ000-CAZ000-240330-

Mesoscale Precipitation Discussion 0988
NWS Weather Prediction Center College Park MD
635 PM EDT Sat Aug 23 2025

Areas affected...Sierra Nevada

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

Valid 232235Z - 240330Z

SUMMARY...Locally heavy showers and thunderstorms will continue
into the evening hours along the foothills and near the crest of
the Sierra Nevada. Scattered areas of flash flooding are likely
which will include localized burn scar impacts.

DISCUSSION...GOES-W IR satellite imagery shows expanding and
cooling convective tops across the Sierra Nevada along with some
of the adjacent foothills. The convection is being strongly aided
by orographic ascent/upslope flow into the terrain coupled with
increasingly divergent flow aloft and an anomalously moist
monsoonal moisture flow pattern.

SBCAPE values of 500 to 1000 J/kg are noted along the western
slopes of the Sierra Nevada with some modest effective bulk shear
in place of 20 to 30 kts. The latest RAP analysis along with IR
satellite imagery shows evidence of a weak upper-level jet streak
lifting north up across the Central Valley of CA which is favoring
some divergent and resulting diffluent flow structures aloft.

This subtle uptick in deeper layer ascent along with the ongoing
orographic and thermodynamic support should favor additional
rounds of heavy showers and thunderstorms near the high terrain
going into the evening hours. Rainfall rates will be capable of
reaching 1 to 1.5 inches/hour given PWs running locally in the
95th+ percentile of climatology and with the aid of upslope flow.

Additional rainfall totals of 2 to 3 inches will be possible
locally through this evening where any repeating cell-activity
occurs, and this will continue to favor a likelihood for scattered
areas of flash flooding. This will include localized burn scar
impacts.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!4Ss8JmzyebEdu7vaw0Og0C1U3OsLnYIXxOKcMGCcFvSqz8Dn3Lw3KvJBnUbuRUa1EEzk=
tOxO41DYm0PQsL9OYApTu4I$  for graphic product...

ATTN...WFO...HNX...REV...STO...VEF...

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

LAT...LON   40931974 40431929 39481892 38041865 36691819=20
            36621906 37612001 39382058 40132048 40802021=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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