Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 PM EST Sun Nov 16 2025

Day 1
Valid 16Z Sun Nov 16 2025 - 12Z Mon Nov 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE SANTA LUCIA
RANGE OF CENTRAL CALIFORNIA...

...16Z update...

No significant changes were made to the previous outlook. The
initial shortwave responsible for the flooding rainfall across
California over the past couple of days has moved inland this
morning and is forecast to lose some of its vigor as it moves into
a downstream ridge. Moisture anomalies have come down compared to
yesterday across the West, and while they remain above average (+1
to +3 standardized PW anomalies), a lack of higher instability and
progressive storm motions should limit the flash flood threat for
most locations. There should be an isolated risk for hourly
rainfall in excess of 0.5 inches from portions of northern to
southern California today.

The next shortwave will bring a cold front to California this
evening and overnight, and with it, a better chance for 0.5 to 1.0
in/hr rainfall rates. The front and heavy rain axis should remain
progressive though, limiting total rainfall to an inch or two for
most locations, although ground sensitivities due to recent
rainfall maintains the Marginal and Slight Risk areas. The greatest
24 hour rainfall potential looks to be within the central to
northern Sierra Nevada where 2 to 3+ inches of rain could fall.

Otto

...previous discussion follows...


A pair of deep shortwaves will impact much of California through
the period today. The one that has been causing heavy rain across
much of southern California is pressing inland this morning. Rates
have come down a bit overnight due to waning instability, but much
of central California and portions of southern California remain in
more-or-less steady light to occasionally moderate rainfall. As
the upper low departs to the east, the steady rain across much of
inland California should diminish through this afternoon. Following
this first shortwave, another vigorous, deepening longwave trough
will track SSE out of the North Pacific and approach the northern
California coast late tonight/early Monday morning. This second
shortwave will have much more upper level energy with it by tonight
than the first does now. This longwave trough will also have some
instability with it. The result will be steady rain associated with
the approaching low plowing into the northern California coast
this evening, then spreading south in the form of a line of
moderate rain with embedded thunderstorms capable of brief periods
of heavy rain. It will cross the Bay area late this evening, then
push south almost to Point Conception by 12Z Mon. The heaviest rain
will push inland, reaching the central Sierra around the same
time.

Much of the Santa Lucia Range in central California have picked up
between 5 and 8 inches of rain over the last week. Continued light
to moderate rain may add another inch through this morning, but the
heavy rains tonight with the cold front will likely drop another
1-2 inches. Rock and landslides have been reported from today's
rain. Thus with shifting winds and heavy rain tonight, it's
probable there may be additional impacts from the storms. In
coordination with MTR/Monterey, CA forecast office, a Slight Risk
upgrade was introduced with this morning's update. Elsewhere the
surrounding Marginal remains unchanged.

...Southwest Utah...

The Marginal Risk area in southwest Utah also remains unchanged.
Upslope flow into the Pine Valley Mountains may cause isolated
instances of flash flooding as the area of rain currently over
southern Nevada pushes east into the region, where enhanced upslope
will cause the rain to intensify. The highest elevations above
8,000 ft or so may see snow, which will limit the flooding
potential at lower elevations.

Wegman

Day 2
Valid 12Z Mon Nov 17 2025 - 12Z Tue Nov 18 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE LOS
ANGELES BASIN OF SOUTHERN CALIFORNIA...

...20Z update...
Some modifications were made to the outlook areas in CA.
Specifically, extended the Slight Risk slightly westward to the
Central CA Coast based on the latest (12Z) CAM guidance as well as
HREF and RRFS 0.50"+/hr and 1.00"+/hr rainfall rate probabilities
on Monday. Meanwhile, also largely based on those HREF and RRFS
exceedance probabilities, have also hoisted a Marginal Risk across
southwest and central portions of AZ.

Hurley

...Previous discussion...
The deep and energetic trough that will be centered off the 
northern California coast at the start of the period will track 
southeast down the coast to over the San Joaquin Valley by early 
Tuesday morning. The trough will cut off into a second upper level 
low to impact the state by Monday afternoon. The heaviest rains 
will be out ahead of this cutoff low, where the overall flow is 
onshore out of the southwest. A line of heavy showers with embedded
thunderstorms will move down the coast starting around Point 
Conception early Monday morning, reaching the L.A. Basin around 
midday. It will take between 2-4 hours for the heavy rain band to 
sweep through. During that time, rainfall rates peaking between a 
half and 3/4 inch per hour in the thunderstorms may cause widely 
scattered instances of flash flooding, especially on the south 
facing slopes of the Transverse Ranges down to the L.A. Basin. For 
this reason, the inherited Slight Risk remains in place with very 
few changes. At least some of the heavy rain will also penetrate 
inland into some of the California Deserts, including around Death 
Valley N.P. Given how recently the area saw heavy rains from 
yesterday, this additional heavy rain may also cause isolated 
instances of flash flooding. Thus, the Marginal Risk was expanded 
north and east to include a small portion of southern Nevada.

Wegman

Day 3
Valid 12Z Tue Nov 18 2025 - 12Z Wed Nov 19 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST AND LOWER GREAT BASIN...

...20Z update...
Based on the guidance trends, have expanded the Marginal Risk area
to include more areas off the Mogollon Rim and into the deserts in
southern and western AZ, southeast CA, and southeast NV. PW values
get near 2 standard deviations above normal in southern-western AZ
(0.75-1.00"), while MUCAPEs climb between 500-750 J/Kg south of 
the Mogollon Rim and into the deserts and Phoenix Metro. This will 
maintain the risk of elevated (0.50"+) hourly rainfall rates Tue- 
Tue night as noted from the RRFS exceedance probabilities (through 
00Z Wed), while also implied from the 12Z RRFS and RGEM hourly and 
3-hourly QPFs. 24hr guidance QPFs have come up from 12Z Tue-12Z 
Wed, especially from the global models, which is a bit concerning, 
yet understandable considering how the upper trough begins to pivot
more slowly as it amplifies from the shortwave energy diving 
southward on its backside. At this point there's still not enough 
confidence from a duration perspective to upgrade to a Slight Risk 
over the lower terrain (all rain) areas south of the Mogollon Rim, 
which would include the Phoenix area, but the potential to do so 
will exist over the next day or so. 

Hurley

...Previous discussion...
A Marginal Risk area across portions of Arizona and southern Utah 
was introduced with this update. The cutoff low that will spread 
heavy rain across the L.A. Basin on Monday will slowly push east 
across southern California through Tuesday. Once again the heaviest
rains associated therewith will be out ahead/east of the low 
center, putting Arizona and Utah in the area most likely to see 
heavy rain. Instability will once again be non-zero, peaking 
between 200 and 400 J/kg, which combined with above normal moisture
will result in an area of training thunderstorms, likely along the
Mogollon north and east of Phoenix. The southerly flow will 
continue across northwest Arizona and into southern Utah, where wet
antecedent conditions from today's rains will support additional 
flash flooding developing with heavy rains in the Pine Valley 
Mountains east to Lake Powell.

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