Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
759 PM EST Fri Nov 14 2025

Day 1
Valid 01Z Sat Nov 15 2025 - 12Z Sat Nov 15 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

...0100 UTC Update...

...Southern California...

The latest Day 1 ERO update included an expansion of the Slight 
Risk area along the Transverse Ranges to the Central CA Coast, 
while a also nudging the Moderate Risk area Slightly westward to 
include more of the Santa Barbara area. The reasons were two-fold. 
First, they incorporate the heavier rain that has already fallen 
(especially areas west of KSBA). Secondly, the slight westward 
adjustment also aligns with the latest high-res guidance 
expectations from recent HRRRs along with the 18Z HREF and 12Z RRFS
ensemble suite. The Moderate Risk area aligns well with the 
highest probability of >0.50"/hr rainfall rates later tonight 
(after 06Z, and especially after 09Z when those probabilities climb
to over 60%), along with where the highest probabilities of >3" 
will fall through 12Z (25-30%) 

Hurley


Day 2
Valid 12Z Sat Nov 15 2025 - 12Z Sun Nov 16 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

20Z Update: The overall synoptic evolution remains unchanged in
the run-to-run variance within guidance today. The prospect for
heavy rainfall will carry forward into Saturday with the low
progression allowing a protrusion of heavier rainfall to impact the
coast to areas inland over the deserts of southern CA/NV into
western AZ and southwest UT. Assessment of the 12z HREF blended
mean QPF footprint and associated prob fields, both neighborhood
and EAS indicate the eastern Transverse and northern Peninsular
Ranges of southern CA will be the beneficiary of the heaviest
precip threat due to the added orographic enhancement as flow
remains mostly orthogonal to the terrain north and east of the LA
metro. HREF neighborhood probs between 40-60% for >5" exist over
portions of the San Bernardino and San Jacinto Mountains spanning
San Bernardino and Riverside counties.

As the disturbances moves eastward, IVT plume will shift inland to
impact the lower deserts in CA and areas further inland towards
NV/AZ and southwest UT generating flash flood concerns with a weak
convective pattern anticipated through the storm life cycle. The
prospects of significant precip on the order of 1" or more are
generally high for the above locations which will be sufficient for
at least widely scattered flash flood concerns as we move into
Saturday afternoon and evening. Probabilities for >2" a bit more
subdued and relegated to the CA/NV border into the Imperial Valley,
but that doesn't mean a few areas across southern NV into the
Colorado River basin can't approach the 2" threshold in this
scenario just given the anomalous airmass involved.

The previous MDT risk was expanded to include more of the San
Jacinto mountains where the highest probabilities for >5" are
located. The SLGT risk was also expanded in the interior given the
latest trends. The MDT was not trimmed in any one location, leaving
the LA metro firmly within the highest risk forecast for the
period.

Kleebauer

..Previous Discussion..

The peak of the heavy rainfall event across southern California
will occur on Day 2/Saturday. The upper level low off the coast
will barrel inland, drawn eastward by the strong shortwave trough
leading it. PWATs are expected to increase to around 1.25 inches,
which is as much as 4 sigma above normal for this time of year.
Meanwhile MUCAPE values could increase to around 250 J/kg near the
coast. As the low moves into central California to near the NV/CA
border in central CA/southwest NV, the plume of heaviest rain will
push inland and slowly weaken with time. Meanwhile, an additional
shortwave will round the low and impact much of southern California
into Saturday night.

Given the expected very wet Friday across much of southern
California, and with the heaviest rains expected to be ongoing at
the start of the period, a Moderate Risk upgrade was also
introduced on Day 2/Saturday. This is in line and for many of the
same areas as on Day 1/Friday. However, unlike Friday's rains,
these rains will have Friday's rains to build upon, worsening the
number, severity, and duration of the heaviest rains across
southern California. Thus, certainty with the Moderate Risk on
Saturday is much higher than on Friday.

As on Friday, as the shortwave and in this case the entire upper
low push ashore, expect occasionally heavy rain with embedded
thunderstorms to continue north and east to impact the southern
Sierras of central California, much of southern Nevada, including
Las Vegas, and much of western Arizona. Rainfall rates will remain
high as heavy rains impact much of these areas. Thus, in
coordination with VEF/Las Vegas, NV forecast office, the inherited
Slight Risk was expanded east to include Esmeralda, southern Nye,
and Clark counties in southwestern Nevada, as well as Mohave County
in Arizona. Urban concerns will be present across the Las Vegas
metro area from the heavy rains as well. The desert soils in this
area should be rather hydrophobic from recent dry weather, which
should support increased runoff, especially early in the day.

In coordination with LOX/Oxnard, CA and HNX/Hanford, CA forecast
offices, a Moderate Risk area was introduced from Point Conception
east through L.A. This especially includes the Palisades fire burn
scar near Malibu, as well as others in the area. Debris flows and
fast moving water are likely as the rainfall drains into the flashy
creeks and streams that drain the Transverse Ranges. Expect the
heaviest rains to impact the L.A. Basin through Saturday morning,
with diminishing rates down to occasional showers and light rain
from Saturday afternoon through the overnight.

Wegman

Day 3
Valid 12Z Sun Nov 16 2025 - 12Z Mon Nov 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
CENTRAL AND NORTHERN CALIFORNIA...

20Z Update: Subtle changes were made to the Day 3 ERO, based on the
latest guidance trends. Still some timing differences during day 3
(Sun-Sun night) as the initial closed mid-level low opens upon
lifting through the ridge across the Great Basin-Central Rockies,
while the next deepening low drops along the northern CA Coast and
Bay Area. One notable trend -- the bulk of the guidance (outside of
the GEM and 12Z RRFS) keeps the heavier rainfall north of the
Central CA Coast and Transverse Ranges.

Hurley

Previous Discussion Below...

As the cutoff low that impacted southern California on Friday and
Saturday moves inland, it will rapidly weaken and quickly become a
non-factor as far as heavy rain is concerned. Nonetheless,
especially early Sunday morning, light rainfall associated
therewith may be ongoing. The bigger event will be a cutoff low
that follows a similar pattern to the first, but much further north
and with less of a tropical connection than the first. The cutoff
low will sag southward from Oregon into northern California. Upper
level energy associated therewith will use what moisture it can
muster to support a progressive cold front that will sweep west to
east across the state. Once again there could be some modest
elevated instability of 300 J/kg or less with the front. Thus,
expect some convection/thunderstorms to be associated with the
front. Those periods of heavy rain when combined with recent heavy
rains from today could lead to isolated instances of flash flooding
in prone areas. Thus, a Marginal Risk was introduced with this
update for much of central and northern California, as well as far
southwestern Oregon.

Wegman


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt