Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Aug 26 2025 18:18:54

AWUS01 KWNH 261818
FFGMPD
NVZ000-CAZ000-270000-

Mesoscale Precipitation Discussion 1007
NWS Weather Prediction Center College Park MD
218 PM EDT Tue Aug 26 2025

Areas affected...eastern CA/western NV

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

Valid 261816Z - 270000Z

SUMMARY...Scattered thunderstorms are expected to develop along
the Sierra Nevada through 21Z, some of which may produce flash
flooding due to slow movement. Stronger cells will be capable of
generating 1-2 in/hr rainfall rates.

DISCUSSION...GOES West visible satellite imagery showed the
development of cumulus and early stages of convective initiation
along portions of the central and southern Sierra Nevada at 18Z.
Despite some remnant cloud cover, the beginning of peak heating
atop the elevated heat source was coinciding with anomalous
tropospheric moisture (90th to 95th percentile for late August).
The region of eastern CA/western NV was situated between a low to
mid-level low offshore of the CA coast and low/trough extending
from eastern OR into central NV. Between these two features was a
section of relatively weak 0-6 km AGL layer winds of 5 to 10 kt
which should contribute to slow storm motions.

Continued heating should lead to the development of 500-1000 J/kg
of instability across the region by mid-afternoon. Thunderstorm
coverage will likely continue to expand over the next few hours
with peak coverage in the 21-00Z time frame. Limited shear should
keep storms disorganized in nature but slow movement and
mesoscale/terrain interactions may allow for a few cells to
exhibit little movement over the course of an hour or two before
subsequent outflow initiates development downstream. Convection
may move into valley locations later in the period. Due to the
moist environment, rainfall rates of 1-2 in/hr (or less than an
hour) will be possible. In addition to overlapping with locations
that have received heavy rainfall over the past 3 days, these high
rates will pose an increased flash flood threat along burn scars,
urban locations or other areas of poor drainage, including the
potential for debris flows in and around sensitive terrain.

Otto

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!884UoJRx-SHbHd-iWAl7AZXOJzMYgmU3TEb-Ntl8fVjl7oR4HHAN4ovVHaZ-_dUkrmpl=
eda8Wca-Of8dPpkj1yCR13o$  for graphic product...

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

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

LAT...LON   39501976 39211916 38491843 37661772 36951705=20
            36151659 35671668 35441727 35421808 35571862=20
            36231878 36731900 37481984 38442031 39302048=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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