301
AWUS01 KWNH 141826
FFGMPD
CAZ000-150015-

Mesoscale Precipitation Discussion 1197
NWS Weather Prediction Center College Park MD
224 PM EDT Tue Oct 14 2025

Areas affected...Southern CA

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

Valid 141824Z - 150015Z

SUMMARY...Locally heavy showers and possibly a few thunderstorms
will maintain a threat for areal flooding impacts including
potential burn scar flash flooding going through early this
evening.

DISCUSSION...A strong upper-level low and an associated frontal
occlusion continues to drop gradually down across southern CA. The
latest GOES-W visible and infrared satellite imagery shows the
leading edge of the cold front and heavy rainfall continuing to
advance through the Los Angeles Basin, with a substantial amount
of post-frontal shower activity maintaining pockets of locally
heavy rainfall.

Rainfall rates with some of the stronger convective elements along
the front and also into the southwest-facing slopes of the San
Gabriel and San Bernadino Mountains have been upwards of 0.50" to
0.75"/hour, and these rates are likely to be maintained at least
for a few more hours as the axis of stronger moisture transport
and convergence with the front continues to advance southeastward
down the coast with an approach on the Peninsular Range.

However, post-frontal instability associated with steepening
mid-level lapse rates closer to the upper low will combine with
low-level cyclonic flow into the terrain to maintain plenty of
shower activity and perhaps a few thunderstorms going through this
afternoon and early this evening. Additionally, the stronger
dynamics associated with the digging upper-level low and influx of
Pacific moisture wrapping northward up into the upslope areas of
the southern Sierra Nevada and also the southern parts of the San
Joaquin Valley will continue to foster areas of heavy rainfall
here which will include a threat for some intense low-top
convective showers.

The heaviest additional rainfall totals should generally be across
parts of the San Gabriel Mountains and especially the San
Bernadino Mountains where as much as an additional 2 to 3 inches
of rain may fall (below snow line) by this evening.

Lowering snow-levels in time will tend to mitigate some of the
runoff potential for the highest terrain, but sufficient rainfall
over especially the Pacific-facing slopes and into some of the
urban areas is expected to maintain concerns through early this
evening for areal flooding impacts and some burn scar flash
flooding. Rockslides and some localized debris flow activity near
and downstream from burn scar locations will continue to be
possible.

Orrison

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

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

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

LAT...LON   36621923 36061849 35241815 34811741 34361675
            33991649 33341652 32631664 32571701 32781734
            33401770 33651827 33791851 33911881 34061919
            34151938 34291957 34441994 35251986 35902019
            36312014