Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Aug 18 2023 21:05:40

AWUS01 KWNH 182105
FFGMPD
NVZ000-CAZ000-190200-

Mesoscale Precipitation Discussion 0943
NWS Weather Prediction Center College Park MD
504 PM EDT Fri Aug 18 2023

Areas affected...Portions of the Sierra Nevada

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

Valid 182103Z - 190200Z

SUMMARY...Locally slow-moving showers and thunderstorms anchored
near the higher terrain of the Sierra Nevada may result in some
isolated flash flooding concerns over the next few hours.

DISCUSSION....Radar and satellite imagery show some slow-moving
and locally anchored convective cells over the Sierra Nevada and
adjacent foothills. The activity is being driven by some
terrain-induced circulations and related differential heating
boundaries coupled with a moist and relatively unstable airmass
pooling up across the higher terrain and adjacent valleys.

There is some forcing of note aloft too around the northeast flank
of a deeper layer trough and associated closed low offshore of
central CA, and this is yielding some relatively divergent flow
aloft over central and northern CA which coupled with the
orographics and thermodynamics is helping to support at least
scattered areas of shower and thunderstorm activity.

Given the rather moist environment overall, some of the stronger
cells will be capable of producing some 1 to 2 inch/hour rainfall
rates, and given the slow-moving cells and instances of
cell-anchoring, it is possible that some storm totals may reach or
exceed 3 inches.

At least an isolated threat of flash flooding will exist from
these cells over the next few hours as a result, and this will
include a threat to any burn scar locations.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!8QajuTCxaI4QS4pLW258H5a-XWrperoI131-nUBPLmoFeKgqg6FlqIUZnPFGzufvznCT=
LQfd_5Jq11w4OQJExyAzFNY$  for graphic product...

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

ATTN...RFC...CNRFC...NWC...

LAT...LON   40862119 40742071 40222018 39591982 39241923=20
            38611901 38221915 38021966 38282000 38632032=20
            39182083 39882134 40662156=20

=3D =3D =3D
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