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FOUS30 KWBC 141600
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1100 AM EST Fri Nov 14 2025

Day 1
Valid 16Z Fri Nov 14 2025 - 12Z Sat Nov 15 2025

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

...16Z update...

...Southern California...

No significant changes to the forecast were needed with a Moderate
Risk maintained across southern California. 12Z sounding data from
NKX showed a PW of 1.36 inches (likely a daily max) with an
ongoing (15Z) moisture surge into eastern Santa Barbara, Ventura
and Los Angeles counties. The early morning (15Z) IVT values along
the coast were near 500 kg/m/s and these values are expected to
weaken during the day today with some lowering of PW values and 850
mb wind speeds. A lingering flash flood threat will continue for
at least the beginning of the ERO period until later this evening
followed by a relative lull toward 00Z. Tonight however, low level
winds will veer toward the south and south-southeast as the
vorticity max mentioned in the previous discussion approaches,
along with a secondary surge in IVT values back toward 500 kg/m/s
and weak instability, supporting the potential for peak hourly
rainfall near 1 inch into the favored terrain.

The focus of heavy rain over the next 24 hours looks to be from
eastern Santa Barbara into Ventura counties, but potential for 2-4
inches (locally higher) will exist throughout the Transverse Ranges
through 12Z Saturday. This threat will continue into the Day 2 ERO
period where a Moderate Risk continues from the existing Day 1
outlook.

...Washington State...

No changes were needed for this update with potential for an
additional 1 to 3 inches for the Olympics and Cascades through 12Z
Saturday. The lower end of that 1-3 inch range is anticipated for
the Olympics with maxima of 3 to perhaps 4 inches in the Cascades
with rates likely staying below 0.5 in/hr. However, wet antecedent
conditions will continue to warrant a Marginal Risk for the region.

Otto

...previous discussion follows...


A deep positively tilted trough off the central California coast
early this morning will cut off entirely from the main jet stream
by this afternoon. A maximum of shortwave upper level energy will
rotate around the southern periphery of the cutoff low, which will
shift it from positive to negative tilt. All the while the cutoff
low will bodily drift east towards the southern California coast.
The result of this pattern will be a plume of moisture tracking NNE
into the southern California coast, roughly orthogonal to the
western Transverse Ranges. The heaviest rains in the Transverse
Ranges are near Point Conception. They will shift eastward with
time along the coast towards the L.A. Basin by this afternoon. The
plume as a whole will weaken with time through the evening hours
due to the aforementioned realignment of the cutoff low and
associated upper level energy. However, on Friday night, as the low
becomes negatively tilted and that upper level shortwave approaches
the coast, rainfall rates will rapidly increase. There has been
some uncertainty as to where the plume of heaviest rain Friday
night will set up, but the latest suite of guidance suggests that
plume will be right over L.A. and points immediately west,
including the hard hit areas from last year`s wildfires around
Malibu and the Palisades.

In coordination with LOX/Oxnard, CA forecast office, a Moderate
Risk upgrade was introduced with this update. This upgrade is
largely for the heavy rain expected through the overnight Friday
night as the approaching shortwave not only increases rainfall
rates, but also it advects some instability into the coast, which
in turn will support elevated thunderstorm activity. Rainfall rates
within the storms may approach 1 inch per hour, especially as those
storms move over the most favored upslope areas on the L.A. facing
side of the Transverse Ranges. Timing will be everything as to how
widespread the impacts will be. However, given the plume`s near
worst- case- scenario position from Malibu and the highly
urbanized L.A. Basin, and the unusual amounts of both moisture
available and instability for November, it`s very possible that the
heavy rain over burn scars and urbanized areas could quickly worsen
resultant flash flooding leading to Moderate level impacts late
Friday night. Further, since the heaviest/worst of the storm will
continue into Day 2/Saturday, the Moderate Risk serves as a likely
"storm total" threat level that both improves continuity in the
forecast, but also encourages preparation during any dry or lighter
rain periods in the L.A. area today.

The rain will continue north into the southern San Joaquin Valley
today, and continuing into the southern Sierras a portions of
southwest Nevada as well. While the rates and total rainfall in
these areas to the lee of the Transverse Ranges will be lighter,
their drier climate will make them similarly susceptible to flash
flooding due to the lower water thresholds needed to support flash
flooding. Given recent drier weather and the worst of the storm
forecast to arrive on Saturday, the area remains in a Marginal Risk
for this update.

...Washington State...

A Marginal Risk across portions of western Washington State was
unchanged with this update as a stalled out cold front becomes a
warm front through the period, resulting in a longer duration
mostly light rainfall across the area, with the favored
upslope/west facing slopes of the Olympics and northern Cascades
most likely to see isolated instances of flash flooding.

Wegman

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...

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...

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