FOUS30 KWBC 240803
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Tue Feb 24 2026

Day 1
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...

Very few changes were needed to the overall risk areas across
California and extreme southwest Oregon. Steady moderate rain is
ongoing from northern California through Oregon and southern
Washington. An area of surface low pressure that is at the leading
edge of a plume of moisture originating from the tropics will move
ashore in Oregon later today. The trailing cold front will guide
the tropical moisture into northern California, leading to multiple
hours of steady rain into the northern Coast Ranges, the Klamath
Ranges, and the northern Sierra Nevada. 

The plume of moisture moving into northern California has also 
brought with it much warmer air. Snow levels have risen to between
8,000 and 10,000 ft; 8,000 closer to the OR border and 10,000 near
I-80. These much higher snow levels moving over the mountains that
have multiple feet of new snow on them from the storms the past 
few weeks is leading to accelerated snow melt. As the rain that has
already begun in this area falls on the snow pack, much of it will
be absorbed. However, after multiple hours of rain through the day,
expect more of it to convert to runoff as combined snow melt and
rainfall. Thus, instances of flash flooding, particularly in the
Slight Risk area of the northern Sierra Nevada mountains and
adjacent foothills to increase into this afternoon and tonight.
Rain will come to an end late tonight, but the flooding could
continue beyond that. Somewhat lesser rainfall amounts are expected
into the northern coastal ranges. There is also significantly less
snowpack in the coast ranges, so there will be less snow to melt
and turn into runoff. For these reasons, the Marginal Risk remains in place.

Wegman


Day 2
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


Day 3
Valid 12Z Thu Feb 26 2026 - 12Z Fri Feb 27 2026

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

...Southeast...

The Marginal Risk across much of the Southeast was dropped with 
this update. The progressive pattern, good northwesterly flow
behind the front, very limited instability, drier than average 
soils, and high FFGs will all work against the development of flash
flooding across the Southeast on Thursday. RRFS and the global 
models suggest a line of storms may develop across Tennessee and 
then sweep south across the Southeast. A line of storms aligned 
orthogonal to the movement of the line rarely, if ever, results in 
flooding. While it's possible for a pair of storms to train over 
the same areas at either end of the line, it seems unlikely that 
will occur over a particularly flood-sensitive area. The flood 
threat is likely less than 5 percent.

Wegman
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