Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
721 PM EST Thu Nov 6 2025
Day 1
Valid 01Z Fri Nov 07 2025 - 12Z Fri Nov 07 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHWESTERN CALIFORNIA AND FAR SOUTHWESTERN OREGON, AS WELL AS THE
OLYMPIC MOUNTAINS AND ADJACENT PORTIONS OF COASTAL NORTHWEST
WASHINGTON...

12Z guidance and the 18Z suite of probability guidance remained on
track for placement/timing of the next surge of enhanced
rainfall...and supported by trends in the short term radar and
satellite imagery. 21Z surface analysis showed a sub-990mb low
pressure translating quickly through the Southeast Gulf of Alaska
toward northern British Columbia with triple point about ready to
press into western Washington. The amplification of the warm sector
will allow for a quick surge of enhanced moisture flux from the
southwest into the Olympic Range with IVT peaking near 700-800
kg/m/s...bringing the bulk of highest rates across the areas solid
potential of up to .5"/hr rates for a couple more hours. Potential
rainfall totals remain in the 2 inch to 4 inch range. Given upper
soil conditions (0-40cm per NASA SPoRT) are nearing 90%, much of
that rainfall can run off and that results in localized flooding
concerns within typical river basins.

Farther south, peak IVT values are expected in the 500 to 600
kg/m/s range as the front continues to push eastward into portions
of northwestern California and southwestern Oregon. The peak IVT
and associated enhanced rainfall rate should be fairly short-
lived...on the order of a few hours or so...before the deep layer
flow becomes more zonal which allows for increased duration of
light to moderate rainfall. Additional 1 inch to 2 inch amounts are
possible...and the soils are saturating resulting in increased
runoff.

No fundamental adjustments were needed to either of the two
Marginal Risk areas given the expected flow patterns into the
terrain.

Bann


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt