Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
732 PM EST Mon Nov 3 2025

Day 1
Valid 01Z Tue Nov 04 2025 - 12Z Tue Nov 04 2025

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

Bann


Day 2
Valid 12Z Tue Nov 04 2025 - 12Z Wed Nov 05 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHWESTERN CALIFORNIA AND FAR SOUTHWESTERN OREGON...

Update...
No changes were made with the daytime update. A Marginal Risk,
covering portions of northern California and far southwestern
Oregon, was maintained. The 12Z HREF shows 24-hour totals
exceeding 3 inches are likely within the highlighted area, with
locally heavier totals over 5 inches possible along the upslope
terrain.

Pereira

Previous Discussion...
The next strong landfalling atmospheric river (IVT > 750 kg/ms)
looks to impact coastal portions of northern CA/far southwestern OR
come tomorrow afternoon, likely peaking in strength in the evening
to overnight period. Unideal low-level flow with the initial
arrival of high IVT in the afternoon now looks to become more
ideally directed perpendicular to the coast/mountains during the
overnight period, suggesting higher confidence of forecast 2-4"
totals (with localized 4"+ most likely near to the coast). While
PWATs of 1.2-1.4" are in the vicinity of the 90th percentile for
early November, instability still looks limited (less than 250
J/kg), and rates will generally peak near 0.25"/hr. This should
relegate any flash flood impacts to locally sensitive terrain (i.e.
burn scars). The inherited Marginal Risk was generally maintained.

Churchill


Day 3
Valid 12Z Wed Nov 05 2025 - 12Z Thu Nov 06 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...

Update...
No significant changes were made to the previous forecast, with the
general consensus of the 12Z guidance showing an additional 2-3
inches, falling mostly in the early part of the period, across
parts of northern California and far southwestern Oregon. This may
prolong runoff concerns, especially over vulnerable areas.

The Marginal Risk over the Olympic was maintained as well, where
many of the models continue to indicate localized amounts exceeding
3 inches.

Pereira

Previous Discussion...
While the aforementioned strong atmospheric river will have peaked
by Wednesday morning, residual flood impacts are possible across
some of the same portions of northwestern CA into early Day 3. In
addition, some flood impacts are possible early farther inland
(upslope portions of the northern Sierras), though rates below
0.5"/hr is still generally expected to limit impacts to burn scars.
A Marginal Risk was generally maintained (shrinking a bit based on
where rainfall is expected to be waning where there is a distinct
lack of burn scars).

In addition, the Marginal Risk for the Olympics and vicinity in
northwest WA was generally maintained, as some models indicate
localized amounts of 3"+. This is judged to be a lower-end Marginal
Risk, as rates should be rather limited with IVT decreasing
substantially by the time low-level flow veers perpendicular to the
coast (no surprise, given the arrival of the cold core low).

Churchill


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt