Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Aug 19 2023 22:31:31

AWUS01 KWNH 192231
FFGMPD
NVZ000-CAZ000-ORZ000-200329-

Mesoscale Precipitation Discussion 0949
NWS Weather Prediction Center College Park MD
630 PM EDT Sat Aug 19 2023

Areas affected...Northern Sierra Nevada into the Klamath Mountains

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

Valid 192229Z - 200329Z

SUMMARY...Scattered slow-moving showers and thunderstorms over the
higher terrain will favor a threat of some isolated flash flooding
heading through the evening hours.

DISCUSSION...Radar and satellite imagery shows slow-moving pockets
of heavy showers and thunderstorms becoming increasingly focused
over areas of the northern Sierra Nevada and also farther back to
the west into northwest CA including the Klamath Mountains. The
convection is being driven strongly by orographic ascent over the
terrain, with smaller scale differential heating boundaries and
terrain-induced circulations providing small scale focus for
convection as a moderate degree of instability also pools up
across the Sacramento Valley.

Some of the slow-moving cells have already been producing 1 to 2
inch/hour rainfall rates, and some additional expansion of
convection will be possible over the next couple of hours as
additional moisture lifts north up across the interior valleys and
adjacent high terrain around the east side of the mid to
upper-level trough just offshore of central CA.

There is a rather diffluent flow pattern noted aloft too over
northern CA given proximity of the offshore energy and the deeper
layer ridging off to the east over the Great Basin.

Expect some spotty 2 to 3+ inch totals to be possible over the
higher terrain, and some areas that do have some burn scars may
potentially see at least an isolated threat for flash flooding as
these storms evolve over the next few hours heading unto the
evening time frame.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!9rmkCtCAWBFzYq8v3EdjcZbM-DUfdiAR4Iszcd2-G0UF7mkxmWMwpxmoSpiwrx9GeKZr=
zf4BWKTVN55xPlZwXQpF4ng$  for graphic product...

ATTN...WFO...EKA...MFR...REV...STO...

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

LAT...LON   42062208 41752121 40852037 39701990 38651950=20
            38241963 38512015 39562060 40292118 40472201=20
            40062260 39442270 39282304 39382337 39732361=20
            40202380 41252375 41862308=20

=3D =3D =3D
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