FOUS30 KWBC 030018
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
718 PM EST Thu Jan 2 2025

Day 1
Valid 01Z Fri Jan 03 2025 - 12Z Fri Jan 03 2025

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

...01Z update...
Maintained the Marginal Risk area with the continuation of a
relatively weak but long duration atmospheric river. Satellite
imagery from late this afternoon supports short-range guidance idea
of an uptick in rainfall rates given cooling cloud tops within a
region of diffluent flow approaches from the eastern North=20
Pacific. The previous adjustments look good and the outlook area=20
remains largely unchanged.

Bann

...16z update...
Forecast remains on track though a few 12z Hi-Res CAM solutions
suggest a slightly northward track of the longer warm advection
showers into the central OR coast. As such, a small northward
inclusion was made to the initial forecast risk area, while the
southern portions across NW CA are sculpted to the favored terrain.

Gallina

A relatively weak, long duration atmospheric river will continue
to impact portions of the Pacific Northwest coast today, shifting
focus from northwest California into far southwest Oregon. While
there is a distinct lack of instability to fuel rainfall rates
beyond 0.25"/hr, tropospheric moisture is still rather elevated
with precipitable water values of 1.0-1.2" (2.0-2.5+ standard
deviations, near the 95th percentile). Two distinct rounds of
precipitation (one from late this morning through mid afternoon,
and another round from late evening through the overnight) are
expected to bring additional rainfall of 3-5" (primarily for Del
Norte county, CA and Curry county, OR). While rapid onset flooding
is generally not expected (given the muted rainfall rates), these
areas (and surroundings) have already received 1-2" over the past
24 hours with USGS streamflow data indicating widespread above
normal to much above normal streamflows (with some even at record
territory for the date), suggesting additional rainfall may lead to
localized flooding impacts.

Churchill


Day 2
Valid 12Z Fri Jan 03 2025 - 12Z Sat Jan 04 2025

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

...2000 UTC Update...
No changes made to the previous D2 Marginal Risk area, based on the
latest (12Z) guidance, which now incorporates the full suite of
high-res CAMs (including the elevated HREF probabilities of hourly
rainfall rates of 0.50+).

Hurley

...Previous discussion below...A strong shortwave and associated
surface low will plow into the coast of California and Oregon on
Friday. Locally heavy rain with rates around 1/2 inch per hour will
be ongoing Friday morning along the coast. The shortwave and low
will move into the coast Friday evening and through the overnight.
This will shift the heaviest rains both southward and inland,
bringing northern portions of the Sacramento Valley, which has been
largely missed with the previous days' rains, into the potential
for heavy rain and higher elevation snow. The Marginal Risk
inherited was left unchanged with this issuance. The heaviest rains
are likely to be Friday morning as the aforementioned shortwave
and surface low approach. Once they move into the coast Friday
evening and overnight, rainfall rates should diminish quite a bit
as the associated moisture moves inland. Any flooding from the Day
2/Thursday period will likely continue into Friday morning along
the Oregon and California coasts...with any minor flooding for the
Sacramento Valley more likely Friday afternoon.

Wegman


Day 3
Valid 12Z Sat Jan 04 2025 - 12Z Sun Jan 05 2025

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

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!-RVptL-YJCCMhmuYGsHHRkoD4sFxf3S8mMh-zE1eHo0W=
klF-FNWMjlYgNdbUPBYsEASpEI4KIQg9bnUMwoZBFRQpeZ8$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!-RVptL-YJCCMhmuYGsHHRkoD4sFxf3S8mMh-zE1eHo0W=
klF-FNWMjlYgNdbUPBYsEASpEI4KIQg9bnUMwoZBGie6eOY$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!-RVptL-YJCCMhmuYGsHHRkoD4sFxf3S8mMh-zE1eHo0W=
klF-FNWMjlYgNdbUPBYsEASpEI4KIQg9bnUMwoZBxl9gGXY$=20

=3D =3D =3D
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