088
AWUS01 KWNH 011521
FFGMPD
CAZ000-012120-

Mesoscale Precipitation Discussion 0002
NWS Weather Prediction Center College Park MD
1020 AM EST Thu Jan 01 2026

Areas affected...portions of southern California

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

Valid 011520Z - 012120Z

Summary...Deep convection along and ahead of a surface cold front
located about 85 miles west of San Diego will continue to foster a
flash flood risk across the discussion area through 21Z/1p Pacific
Time.

Discussion...Areas of deep convection persist especially in/near
terrain-favored upslope regions of the discussion area currently.
The convection was being supported by mid-level cooling (which has
fostered a pool of ~250 J/kg SBCAPE over Pacific and near-coastal
regions of the discussion area), orographic ascent (sponsored by
25-30 knot 850mb flow against Transverse and Peninsular coastal
ranges), and 1-1.3 inch PW values - supporting efficient rainfall
processes in/near convective activity.  Recent MRMS/observational
data depicts an uptick of rain rates in both Los Angeles Metro
(into the 0.4 inch/hr range) and across San Diego County (where
0.5-0.8 inch/hr rates were estimated).  These rain rates were
occuring over urban areas and near sensitive terrain from prior
flash flood impacts, burn scars, and terrain.  Flash flooding
remains possible in these areas in the short term.

Models/observations suggest that the aforementioned Pacific cold
front will traverse the region from west to east and bring a
substantial decrease in flood/flash flood potential over time.
For the Los Angeles area and Transverse Ranges, this risk will
likely extend into the 18-20Z timeframe before decreasing some.
The front will take a bit longer to cross San Diego and adjacent
Peninsular Ranges (around 21Z or so).  Flash flooding will remain
possible through the aforementioned timeframes.

Cook

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...HNX...LOX...PSR...SGX...VEF...

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

LAT...LON   35241857 35091802 34771717 34251662 33621619
            32831597 32531613 32461695 32551746 33081815
            33981872 34691879