905
AWUS01 KWNH 132136
FFGMPD
CAZ000-140900-

Mesoscale Precipitation Discussion 1222
NWS Weather Prediction Center College Park MD
435 PM EST Thu Nov 13 2025

Areas affected...western Transverse Ranges into central CA and
northern Sierra Nevada

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

Valid 132133Z - 140900Z

Summary...Flash Flood potential will extend into the evening and
overnight hours from portions of the northern Sierra Nevada into
much of central CA and the western Transverse Ranges. Peak hourly
rainfall of 0.5 to near 1.0 inches is expected along with peak 12
hour rainfall values of 2 to 4 inches through 09Z.

Discussion...21Z radar imagery and GOES West infrared satellite
imagery showed a band of moderate to heavy rain extending from
Monterey Bay and the northern Santa Lucia Range into the eastern
Pacific, out ahead of a Pacific cold front. The cold front has
been steadily advancing east since this morning and was preceded
by an atmospheric river containing max PW values of 1.3 to 1.5
inches along the coast and just offshore. Within this plume were S
to SSW 850-700 mb winds of 40 to 50+ kt, supporting earlier hourly
rainfall of 0.7 to near 1 inch across the Santa Cruz Mountains. A
number of reports of flooding and debris flows have been observed
since earlier this morning, in and around the San Francisco Bay
region down to Monterey Bay.

As a closed low centered near 41N 128W and southward extending
trough/low, as seen on water vapor imagery, continues to advance
closer to the coast, some weakening of the mid-level low is
expected as the system continues to mature and evolve. The cold
front will maintain a slow but steady movement toward the east but
a ~10 kt weakening of the 850-700 mb winds is expected as the
moisture axis advances downstream ahead of the cold front. This
weakening will correspond to a lowering of IVT values over land,
maxing out in the 600-800 kg/m/s range through 09Z Friday.

Occasional peak hourly rainfall of 0.5 to ~1 inch is expected to
be focused within locations where low level winds will focus into
S to SW facing terrain. The most likely locations for these higher
rates will be within the Coastal Ranges and Sierra Nevada but any
slowing/stalling of a band of weak convection across the San
Joaquin Valley will also have the potential to produce these
higher rates given the moisture already present and weak MLCAPE up
to 500 J/kg forecast by the RAP.

Most instances of flooding/flash flooding are expected to be
minor, but will be most probable across urban and other flood
prone locations. However, localized occurrences of more impactful
flash flooding will be possible where overlap of heavy rain occurs
with any sensitive burn scars and terrain with potential for
debris flows.

Otto

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

ATTN...WFO...HNX...LOX...MTR...REV...STO...

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

LAT...LON   40682176 40442144 39982074 39642050 39382033
            39082023 38842014 38692005 38551994 38481986
            38361970 38241972 38131973 38081971 37921946
            37821936 37701937 37601929 37511915 37431904
            37151884 36991877 36861884 36661952 36832010
            36462052 35822041 35232021 34941972 34421932
            34271951 34302044 34462098 35252146 35842184
            36472222 37032175 38842141 40302192