AWUS01 KWNH 030901
FFGMPD
CAZ000-031800-

Mesoscale Precipitation Discussion 0003
NWS Weather Prediction Center College Park MD
400 AM EST Sat Jan 03 2026

Areas affected...The Western Transverse Ranges of Southern
California

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

Valid 030900Z - 031800Z

SUMMARY...Flash flooding is likely across the Western Transverse
Ranges this morning as rainfall rates to 1 inch/hour lead to flash
flooding and landslides, especially around burn scars.

DISCUSSION...A highly dynamic weather pattern has set up across
portions of California. A deep upper level low and associated
upper level shortwave are approaching the West Coast. The
shortwave is tapping into a moisture plume set up off the coast of
Mexico and advecting some deeper tropical moisture towards the
coast. PWATs will be increasing to over 1 inch, which is 2.5 sigma
above normal for this time of year. Thus, as a series of surface
fronts (not shown) approach, the addition of upper level energy
from the shortwave and abnormal moisture will allow for rainfall
rates to increase to up to 1 inch per hour into the western
Transverse Ranges this morning.

850 mb southerly flow of 20-30 kts will support increasing upslope
enhancement of the rainfall, which will support the heavier
rainfall locally from Lompoc east through Oxnard, including Santa
Barbara. NASA Sport imagery shows soils are above the 90th
percentile compared to climatology across the area. Thus, a brief
period of heavier rain rates, expected later this morning, should
be all that is needed to fully saturate the soils. Additional
rainfall from there will quickly convert to runoff. This runoff
will fill small streams and creeks, as well as increase the
potential for landslides. Downstream flash flooding, particularly
below the numerous burn scars in the area, is likely through this
morning. The area of heavy rainfall, while progressive, will still
be slow to track eastward down the coast. Any one area should see
anywhere from 3 to 6 hours of rain, heavy at times, before the
plume moves off to the east.

The latest CAMs guidance suggests that by the time the area of
heavy rain arrives into the heart of the Los Angeles basin this
afternoon, it should both be weakening and narrowing. Thus, while
Los Angeles is expected to pick up some rain later this afternoon,
rainfall rates are not expected to be quite as heavy, so impacts
should be somewhat limited.

Wegman

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

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

LAT...LON 35572092 35572058 35572025 35462016 35311989
35091962 34861946 34751915 34641845 34521835
34121866 34001899 34161953 34392077 35432121
35492116
$$
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