Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Thu Sep 25 2025 20:25:38

AWUS01 KWNH 252025
FFGMPD
NVZ000-CAZ000-260215-

Mesoscale Precipitation Discussion 1138
NWS Weather Prediction Center College Park MD
424 PM EDT Thu Sep 25 2025

Areas affected...Sierra Nevada into portions of central NV

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

Valid 252023Z - 260215Z

SUMMARY...Intense heavy rain cores are expected to result in at
least isolated flash flooding into the afternoon and early evening
hours from the Sierra Nevada into portions of central NV. Hourly
rainfall of 1 to 2 inches is expected but with sub-hourly totals
of 0.5 to 1.0 inches in 15-30 minutes.

DISCUSSION...GOES West visible satellite imagery and ENTLN
lightning data showed a few widely scattered thunderstorms from
the Sierra Nevada into portions of south-central NV. The storms
were located to the north and east of the 700 mb reflection of a
mid-level low over CA, with highly anomalous moisture (2 to 3+
standardize PW anomalies) extending from the low center into much
of NV. VAD wind data at 700 mb and RAP guidance showed 20-30 kt
wind speeds at 700 mb over the lower CO River Valley into southern
NV but weakening to ~10 kt over central and western NV (some
degree of speed convergence).

Deeper layer mean wind speeds were weak (<10 kt) under and north
of the mid-level low which will result in slow cell motions.
Placement of the mid-level low to the west of the Sierra Nevada
and southerly flow to its east, aligned with the orientation of
the Sierra Nevada range will likely result in some repeating
rounds of thunderstorms across the higher terrain where 500-1000
J/kg of instability is forecast to expand by later this afternoon.
Farther to the east, from western to central NV, favorable
unidirectional southerly flow will increase the potential for
training and brief backbuilding of cells where locally stronger
low level flow exists. Due to the anomalous moisture in place,
both areas of CA and NV will have the potential for high rainfall
rates, hourly totals of 1 to 2 inches and 0.5 to 1.0 inches in
15-30 minutes, which should result in at least isolated areas of
flash flooding into the evening hours.

Otto

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!_nZGtwH_GXyul5EIDi8z1LU22llk81oAmhDmVrjBphJ_-ppZR8Z6Gytx8F2BTSt-WyXv=
EPAlC_RBSuEqhOHi3m7piPQ$  for graphic product...

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

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

LAT...LON   39871830 39761745 39141638 37841613 37041697=20
            36121781 35801851 35881877 36341898 36751920=20
            37171968 37512003 37962031 38332050 38912031=20
            39431975 39761896=20

=3D =3D =3D
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