FOUS30 KWBC 230803
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Mon Feb 23 2026

Day 1
Valid 12Z Mon Feb 23 2026 - 12Z Tue Feb 24 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHWESTERN WASHINGTON, ALL OF WESTERN OREGON, AND INTO PORTIONS
OF NORTHERN CALIFORNIA...

A deep positively tilted trough extending from British Columbia
southwest towards the Hawaiian Islands will be flanked on its
southeast side with a 170 kt southwesterly jet. This jet will be
aimed at western Washington State for the first half of the day on
Monday. Meanwhile, a weakening surface low embedded within that
trough will help direct an atmospheric river (A.R.) which extends
from the tropics east of Hawaii northeast into the West Coast. As
the jet streak reorients, a surface low will develop along that
plume, locally enhancing rainfall rates into southern Oregon and
northern California Monday night. Meanwhile, snow levels will rise
to above 8,000 ft. The combination of locally heavy rain as the low
and its associated cold front move ashore and snowmelt through the
coastal mountains from northern California through southern
Washington will likely raise local stream, creek, and river levels
such that isolated flash flooding is possible, especially in any
more flood-prone areas. The inherited Marginal Risk was mostly
unchanged, but a slower southward progression did require some
trimming of the inherited Marginal Risk area north out of the Bay 
Area, as it no longer looks like meaningful rain will reach that 
far south during this period.

Wegman


Day 2
Valid 12Z Tue Feb 24 2026 - 12Z Wed Feb 25 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHERN SIERRA NEVADA MOUNTAINS AND ADJACENT FOOTHILLS...

Few changes were needed to the inherited risk areas across northern
California. The cold front associated with a low that will move
inland and dissipate into Oregon will keep a steady stream of
subtropical Pacific moisture moving into northern California for
much of the day Tuesday. The rain will be aided, in part, by the
persistent 150 kt jet, aimed at southwestern Oregon. The rain 
shield looks to stay more over northern California and not get 
quite as far south into the southern Sierras, so the inherited 
Slight and Marginal Risks were trimmed on their south sides. A few 
other notable changes were somewhat of a decrease in total rainfall
expected, due in part to the expectation of less elevated 
convection than previous forecasts. However, given the recent 
multiple feet of snow that fell into the northern Sierras over the 
past week or two, there is plenty of snow to melt as snow levels on
Tuesday remain between 8,000 and 9,000 feet across all of the 
northern Sierras. Thus, while confidence in Slight Risk level 
impacts occurring has decreased a bit, there still remains enough 
to maintain the Slight across the northern Sierra Nevada and their 
adjacent foothills. The rain will continue pushing south but 
rapidly diminish in intensity Tuesday night. This combined with 
falling snow levels by Wednesday will end the flash flooding 
threat, though river levels will likely remain elevated through late week.

Wegman


Day 3
Valid 12Z Wed Feb 25 2026 - 12Z Thu Feb 26 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman
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