FOUS30 KWBC 220800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sun Feb 22 2026

Day 1
Valid 12Z Sun Feb 22 2026 - 12Z Mon Feb 23 2026

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

Wegman


Day 2
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 extends from around Vancouver
Island southwest down past the Hawaiian Islands at the start of the
period 12Z Monday. This trough extending that far south will draw
deep tropical warmth and moisture and rapidly draw it northeastward
into the Pacific Northwest on a 170 kt southwesterly jet. At the
surface, a low west of Vancouver Island will track southwestward
and merge with a weaker, smaller low. This will allow an impulse of
tropical moisture departing from the Hawaiian Islands to track into
the Oregon and Washington coasts by Monday night as a weak surface low
develops within the moisture plume.  

Rain associated with the onshore flow will impact mainly the
Washington and Oregon coasts during the day Monday, gradually
sinking south in response to the approaching impulse of moisture
from the tropics. The low and associated heavy rain moves into the
coast near the OR/CA border Monday night. Since its track is
somewhat parallel to the coast, a rather small percentage of the
moisture will penetrate into the interior, so the coastal mountains
are likely to take the lion's share of the associated rain. The
warmth moving into the coast will allow snow levels across much of
Northern California to rise above 8,000 ft Monday night around the
OR/CA border, and above 10,000 ft further south towards the Bay
Area and Sacramento. This will initiate the snowmelt process across
all of the coastal Ranges and Sierra Nevada Mountains. The
inherited Marginal Risk remains unchanged for this area as recent
cold and snow has kept stream and creek levels at low levels. Thus,
the rain and snowmelt will begin to contribute to stream rises but
flooding should remain rather isolated as much of the rain gets
absorbed into the snowpack.

Wegman


Day 3
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...

A deep positively tilted trough that extends from Vancouver Island
southwest through the Hawaiian Islands will remain the primary
steering mechanism for an atmospheric river from the tropics and 
into Oregon. This moisture will be aided by a 150 kt southwesterly 
jet. This jet and the downstream ridging over the Southwest will 
flatten out as the trough cuts off into an upper low well north and
east of Hawaii. This will cut off the feed of tropical moisture 
into the West Coast by Tuesday night. Thus, the period of heaviest 
rains will be primarily during the day Tuesday. A surface low 
Tuesday morning will be near where the coast meets with the CA/OR 
border. Since the rain associated with the low has origins in the 
tropics, associated elevated instability, anomalous warmth and 
moisture will all move into northern California. Snow levels will 
rise to over 8,000 ft over much of northern California, and over 
9,000 ft across much of the northern Sierra Nevada. This will 
result in occasionally heavy rain associated with elevated 
convection that quickly tracks northeastward into northern 
California. Rainfall rates could exceed 3/4 inches per hour at times.

Meanwhile recent abundant heavy snow from abnormally low snow 
levels will be replaced with this tropical moisture and warmth. The
now very high snow levels will initiate the snow melting process. 
When the heavy rain moves in over that snow pack, expect initial 
absorption of the rain by the snow pack Tuesday morning, but as 
more rain moves in Tuesday afternoon, it's likely that areas of 
less deep snowpack, such as the foothills of the Sierra Nevada and 
the Shasta, Siskiyou, and Salmon Ranges will all see rapid runoff 
occur, sending local streams, creeks, and rivers rising very 
quickly. This will be the combined result of both heavy rain and 
fast snow melt. Given the expected rapid rises from both small 
creeks to large rivers, flash flooding is likely to be a bit more 
widespread. Thus, a Slight Risk upgrade has been hoisted for the 
Sierra Nevada foothills, where the heaviest rains are expected due 
to the greatest magnitude of upslope. However, heavy rains into the
other Northern California ranges may necessitate an expansion of 
the Slight Risk with future updates.

Wegman
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