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FOUS30 KWBC 130840
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Thu Nov 13 2025

Day 1
Valid 12Z Thu Nov 13 2025 - 12Z Fri Nov 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN AND CENTRAL CALIFORNIA INCLUDING THE BAY AREA AND PARTS OF
THE CENTRAL VALLEY AND SIERRA NEVADA...

Models remain consistent in depicting a heavy rainfall scenario
over portions of California today. A strong fetch of Pacific
moisture will migrate inland today (perhaps beginning as early as
12Z this morning in coastal areas) ahead of a stout mid-level wave
centered over 40.3N/128.7W. This wave will make slow eastward
progress throughout the day while also gradually cutting off from a
belt of stronger westerlies over the Pacific Northwest and
southwestern Canadian Provinces. 40-65 kt south-southwesterly 850mb
flow and 1-1.3 inch PW values all support orographically enhanced
heavy rainfall especially along upslope areas of the Sierra and
coastal ranges near/north of San Francisco. Widespread areas of 4-6
inch 24-hour rainfall totals are expected from near Redding through
Chico to east of Sacramento. Locally heavy amounts (exceeding 3
inches) are also likely north of San Francisco and along Route 1
through Monterrey. Sensitive areas/burn scars are most likely to
experience initial impacts, although urban areas in/near San
Francisco, Oakland, and Sacramento are likely to experience impacts
especially beginning in the morning hours.

The focus of onshore flow will gradually shift southward toward the
western Transverse Ranges late in the forecast period (toward 12Z
Friday). Continued onshore flow (associated with the southward
translating low-level jet stream will contribute to potential
local amounts of 2-3 inches across portions of Santa Barbara County
through that time frame.

The Pacific Northwest will also be a second area of heavy rainfall
potential through the forecast period. Despite the mid/upper low
cutting off west of California, models depict 30-45 knots of
southwesterly flow oriented favorably for upslope against the
Cascades and Olympics for most of the forecast period. Models
suggest potential for 2-4 inch rainfall totals to occur through 12Z
Friday below snow level. Although initial ground conditions do not
appear to be susceptible to runoff initially, the persistent heavy
rainfall will likely elevate water levels and pose isolated
instances of flooding/flash flooding during the forecast period.

Cook

Day 2
Valid 12Z Fri Nov 14 2025 - 12Z Sat Nov 15 2025

...THERE IS A SLIGHT RISK FO EXCESSIVE RAINFALL FOR THE TRANSVERSE
RANGE OF SOUTHERN CALIFORNIA...

A front will continue to make southward progress toward the
Transverse Ranges at the beginning of the forecast period, with
strong onshore flow (around 25-35 knots at 850mb) continuing to
foster upslope and orographically enhanced rainfall at 12Z Fri.
Over time though, this flow will slacken partially due to the
cutting off and retrograding mid/upper low west of the California
coast. The heavy rainfall threat will lessen substantially during
the day as a result, with only terrain-favored areas experiencing
what should be an isolated risk of excessive rainfall.
Slight Risk areas are maintained for this outlook per the previous
forecast, but have been confined to portions of Santa Barbara and
Ventura Counties for the morning rainfall activity.

Late in the forecast period, models suggest another uptick in heavy
rainfall potential approaching portions of the Los Angeles Basin
and adjacent eastern Tranverse and San Diego County Mountains.
Timing on the onset of this activity is a bit uncertain, and the
bulk of this second surge of rainfall should hold until D3/Sat. A
Marginal Risk is maintained in these areas to address this
secondary threat.

Lastly, strong southwesterly flow will impinge upon the Olympics
and Cascades for a second consecutive day Friday. This
orographically enhanced heavy rain scenario will promote areas of
an additional 1-2 inches of rainfall (with locally higher totals).
With antecedent rainfall expected to fill area watersheds on
D1/Thursday, the additional rainfall could cause isolated
instances of flooding/flash flooding expecially in sensitive and
low-lying areas. A Marginal Risk area has been added to account for
this threat.

Cook

Day 3
Valid 12Z Sat Nov 15 2025 - 12Z Sun Nov 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS A LARGE PART
OF SOUTHERN CALIFORNIA...

Strong onshore flow will redevelop across coastal ranges of
southern California as a mid/upper low over (initially cutting off
and retrograding over Pacific waters on D2/Fri) begins to advance
slowly eastward during the forecast period. Models depict modest
uncertainty with respect the timing of this system, however.
Despite the uncertainty, south-southeasterly low-level flow will
aid in advecting impressive moisture of tropical origin (with 1.5
inch PWAT values) toward both coastal areas and portions of the
Lower Colorado River Valley. The combination of this moisture,
orographic ascent, and eventual cooling aloft should result in
several areas of heavy rainfall, with 2-4 inch totals expected (and
locally higher amounts).

Ordinarily, a setup like this would necessitate an upgrade to
higher excessive rainfall probabilities and perhaps even a
categorical upgrade particularly for the Transverse Ranges.
Lingering uncertainties regarding timing of precipitation onset and
typical difficulties in forecasting mesoscale phenomenon at 3-day
timeframes are contributing factors to holding off on an upgrade at
this time. An upgrade may be needed in later outlooks - especially
with potential for heavy rainfall impacting a number of local burn
scars north of the Los Angeles Metro area.

Farther north and east, models depict a substantial increase in
moistening and precipitation chances toward the southwestern Great
Basin and Lower Colorado River Valley. There`s some uncertainty
regarding how moist the low-levels will get in these areas due
model handling of the airmass over the northern Gulf of California.
Relatively fast flow aloft will contribute to quick movement of
convection also. A large area of Marginal and Slight Risk areas
were maintained for this outlook, though any increases in low-level
moistening/instability will likely result in an increase in flash
flood potential that will need to be addressed with spatial
expansions of risk areas.

Cook

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