Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sun Aug 24 2025 19:00:48

AWUS01 KWNH 241900
FFGMPD
NVZ000-CAZ000-250100-

Mesoscale Precipitation Discussion 0991
NWS Weather Prediction Center College Park MD
300 PM EDT Sun Aug 24 2025

Areas affected...Sierra Nevada...Western Nevada

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

Valid 241900Z - 250100Z

SUMMARY...Deep layer monsoonal moisture entrenched across large
areas of the Southwest and into the Great Basin will favor showers
and thunderstorms through this afternoon with locally high
rainfall rates. Scattered areas of flash flooding will be likely
which include potential impacts to burn scar locations.

DISCUSSION...The deeper layer subtropical ridge near the Four
Corners region remains in a conducive position to drive and
sustain the transport of monsoonal moisture up across southern and
eastern CA including the Sierra Nevada and adjacent areas of the
Great Basin. The latest CIRA-ALPW data shows moisture near or
above the 90th percentile of climatology in the 700/500 mb and
500/300 mb layers respectively, with the 12Z RAOB sounding at KREV
(Reno, NV) showing an impressive PW of 0.98 which is near a record
for the date.

This moisture coupled with placement of mid-level vort energy near
the western foothills of the central Sierra Nevada and modest
deeper upslope flow over the higher terrain will combine with
increasing boundary layer instability for scattered to eventually
broken areas of heavy shower and thunderstorm activity once again
for this afternoon. The latest GOES-W Day Cloud Phase RGB
satellite imagery along with LightningCast data suggests CI
(convective initiation) is imminent along the terrain of the
Sierra Nevada.

Convection is also expected to develop farther east across the
plateau areas of western NV to the east of the terrain where there
will also be a combination of orographics and diurnal heating
within this very moist monsoon pattern to support locally heavy
showers and thunderstorms.

Given the high moisture environment, rainfall rates up to 1.5
inches/hour will be possible, with some localized storm total
amounts by late this afternoon of 2 to 4 inches possible where any
cells tend to become more terrain-focused. Scattered areas of
flash flooding are likely going through this afternoon, and there
will be localized concerns for burn scar impacts.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!-chfZMgdqkkHXqNCzQafAo4wMaeKktUOQSGJ94k_fUZxLvJ6v_f_0PN5-O35REqj2g3Z=
3K0HPjRbfnc9Teb1D9pZIP4$  for graphic product...

ATTN...WFO...HNX...LKN...MFR...REV...STO...VEF...

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

LAT...LON   41782021 41451909 40421804 39771769 38961699=20
            37921676 37261712 36391738 35751751 35501782=20
            35421828 35891866 36621899 37781987 38842074=20
            40212148 41362128=20

=3D =3D =3D
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