Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Wed Jul 24 2024 18:17:03

AWUS01 KWNH 241816
FFGMPD
NVZ000-CAZ000-250015-

Mesoscale Precipitation Discussion 0717
NWS Weather Prediction Center College Park MD
215 PM EDT Wed Jul 24 2024

Areas affected...Portions of the Central/Southern Sierra Nevada
and adjacent foothills

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

Valid 241815Z - 250015Z

SUMMARY...Showers and thunderstorms will be initiating and
expanding in coverage over portions of the central and southern
Sierra Nevada and the adjacent foothills over the next several
hours. There will be concerns for slow-moving and locally
terrain-anchored convection that may produce heavy rainfall
amounts and concerns for flash flooding.

DISCUSSION...GOES-W visible satellite imagery is showing a gradual
uptick in CU/TCU development over the Sierra Nevada, with hints of
convective initiation beginning to take place locally. A favorable
environment is in place today for slow-moving and locally
terrain-anchored convection as a combination of weak deep layer
steering flow and proximity of orographically induced differential
heating boundaries/circulations couple with strong diurnal
heating/boundary layer instability for work convective development
and localized persistence.

SBCAPE values have risen already to locally 1000 to 1500 J/kg,
with areas of the southern Sierra Nevada seeing the greatest
magnitudes of this currently. The airmass is also quite moist with
CIRA-ALPW data showing a rather deep column of elevated moisture
which extends well into the 500/300 mb layer. The PWs are locally
in the 95th percentile of climatology and exceeding 3 standard
deviations above normal.

This combination of moisture and instability over the terrain with
a substantial orographic focus for ascent is expected to yield
showers and thunderstorms capable of producing heavy rainfall
rates that may reach 1 to 2 inches/hour. The latest hires CAMs are
very likely underdone given the set-up, but the NAM-conest does
suggest some spotty 2 to 3 inch rainfall totals today which
appears to be more reasonable.

Isolated to widely scattered instances of flash flooding will be
possible, and this threat will mainly apply to the burn scar
locations of the Sierra Nevada, but given the rugged terrain and
high rainfall rates in general, there will be concerns for some
locally enhanced runoff where any of these slow-moving areas of
convection occur today.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!8tv4Yzdi27hS_2qcgZGRZXEJK8DqPMAtX_vS-FjoKBf_Dk-6jeLYZ_PkBQTBCSrrTwqg=
LoD-nhYFQuWM8JPREhj0Wsk$  for graphic product...

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

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

LAT...LON   40131972 39941907 39641858 38841795 37991754=20
            36821732 35741750 35141804 35151858 35611893=20
            36781943 38072050 38792079 39652068 40062026=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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