Mesoscale Precipitation Discussion 0054
NWS Weather Prediction Center College Park MD
501 PM EST Tue Feb 06 2024

Areas affected...Southern California

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

Valid 062200Z - 070600Z

SUMMARY...Localized flash flooding will remain over southern CA
over the next several hours. Peak rainfall rates near 0.5 in/hr
are expected but should remain very localized across the region.
However, saturated grounds will continue a threat for additional
flooding and debris flows.

DISCUSSION...GOES West water vapor imagery and KSOX reflectivity
at 2120Z showed a low level vorticity max spiraling into the Los
Angeles metro, out ahead of the base of a large scale mid to upper
level trough advancing eastward across CA. Water vapor imagery
also showed a pair of mid to upper level vorticity maxima offshore
of southern CA with locally moderate to heavy rain ongoing across
eastern Ventura County into Los Angeles County in association with
lift ahead of the vorticity maxima. Cold mid-levels, 500 mb
temperatures near -26 C, were supporting weak instability near 500
J/kg along the coast as seen on the latest SPC mesoanalysis.
Earlier rainfall rates peaking near 1 in/hr were observed in the
Los Angeles metro, but precipitable water values are beginning to
lower and better large scale forcing has shifted to the east.

Across Santa Barbara, Ventura and Los Angeles counties, slow
movement of moderate to heavy rain is expected ahead of the
offshore vorticity maxima with 0-6 km mean winds of less than 10
kt across the region and only slow translation of forcing. Farther
south down the coast, onshore 850-700 mb winds of 20-30 kt into
Orange and San Diego counties should maintain over the next
several hours. Scattered showers and perhaps a thunderstorm are
expected to impact the region through early overnight and while
wetter antecedent conditions were located farther north up the
coast, localized potential for flash flooding from hourly rainfall
up to about 0.5 inches will still remain.

The entire southern CA coast to roughly 6000 ft in elevation along
the Transverse and Peninsular Ranges will continue to have a
localized threat for flash flooding and debris flows from heavy
rainfall. Additional rainfall totals through 06Z of 1 to 1.5
inches are expected.

Otto

ATTN...WFO...LOX...SGX...

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

LAT...LON   34801981 34581917 34281807 34261713 33991683
            33451658 32811648 32581641 32391643 32341697
            32411720 32811747 33261777 33441800 33621851
            33791878 33961917 34171968 34432014 34722010