AWUS01 KWNH 151010
FFGMPD
CAZ000-152209-

Mesoscale Precipitation Discussion 1224
NWS Weather Prediction Center College Park MD
510 AM EST Sat Nov 15 2025

Areas affected...portions of southern California

Concerning...Heavy rainfall...Flash flooding likely

Valid 151009Z - 152209Z

Summary...Heavy rainfall will become more likely - especially
beginning around the 14Z/6a Pacific timeframe. Rain rates
reaching 1 inch/hr are possible with this activity. Flash flood
potential will increase - especially across burn scars and other
low-lying, urban, and sensitive areas.

Discussion...Convection was beginning to deepen and move northward
across open waters adjacent to the southern California coastline
this morning. This convection was materializing in response to a
deep cutoff low centered near 32N, 124.5W that was beginning a
slow migration eastward toward the discussion area. On the
eastern periphery of this low, a very moist airmass was in place,
with PW values ranging from 1 inch near coastal areas to 1.6 inch
just offshore. Weak instability and modest forcing for ascent
over land areas are limiting factors for heavier rainfall
potential in the short-term and toward 14Z or so.

Later this morning, a belt of stronger southerly flow at 850mb
will develop toward coastal areas extending from the LA Basin
southward along the San Diego County coastline. Some of this flow
will interact favorably with coastal ranges (particularly the
Transverse) to promote an increasing risk of heavier rainfall.
Quick moistening is also expected to accompany this flow over
those areas. Rain rates should come up in tandem with approaching
ascent and orographic lift, and areas of 1 inch/hr rain rates
should occur on a more frequent basis. At least a few instances
of flash flooding/excessive runoff are expected. Furthermore,
these rain rates should occur over local burn scars, prompting
dangerous debris flows in some areas. Locally significant impacts
will become possible in this regime.

Heavy rain potential will persist through at least 2200Z/1p
Pacific Time today and beyond as the upstream mid-level wave makes
only slow/gradual progress toward land areas.

Cook

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

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

LAT...LON 35351981 35191853 34841736 34211654 33441614
32791601 32561639 32561714 33101753 33641831
34191949 34552052 35082065

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