163
FXUS66 KPQR 051754 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
953 AM PST Fri Dec 5 2025

...Updated aviation discussion...

.SYNOPSIS...A steady succession of frontal systems will keep
conditions wet through the weekend and much of next week. The most
notable period continues to focus on Monday through midweek, when a
prolonged atmospheric river may bring significant rainfall and
rising rivers across southwest Washington and northwest Oregon.

.DISCUSSION...Now through Thursday...A more robust frontal
system is moving inland early this morning, bringing widespread rain
to the region. This feature carries a stronger plume of moisture
than yesterdays system, with integrated vapor transport values
generally running in the 500-700 kg/ms range. This is enough to
support persistent rainfall through the day, including areas farther
south that were largely missed during the previous event. Rainfall
from now through 5 AM Saturday is expected to total about 0.25 to
0.50 inches across interior lowlands. Totals will be notably higher
along the coast, generally in the 1.0 to 1.5 inch range, with 2 to 3
inches common across the Coast Range and Cascades. Winds today will
turn breezy from the southwest, with gusts most frequently reaching
25 to 35 mph through most of the day. Expect the frontal passage to
arrive around 7-10 AM today.

Showers linger into Saturday as a westerly flow pattern persists.
Another frontal wave will arrive Sunday and bring yet another round
of steady rainfall to the region. Ensemble guidance suggests IVT
values with Sundays system in the 300-500 kg/ms range, producing a
widespread soaking. Rainfall totals from Saturday through sunday are
currently projected to fall in the 0.5 to 1.0 inch range across the
interior lowlands, with 0.75 to 1.0 inches along the coast and 1 to
2 inches in the Coast Range. The Cascades are expected to receive
roughly 1.5 to 3.0 inches, except for the Lane County Cascades where
amounts are closer to 0.5 to 1.5 inches. Forecast confidence in the
exact high and low ends of these ranges remains moderate. Widespread
impacts are not anticipated through Sunday; however, if rainfall
rates sustain around 0.2 to 0.3 inches per hour for several hours, a
few faster-reponding basins, such as the Grays at Rosburg and the
Willapa River, could rise quickly.

Attention then turns to the Monday-Wednesday period, where models
continue to suggest a multi-day atmospheric river. Over  the past
several cycles, ensembles have become increasingly consistent in
highlighting two distinct surges of moisture: one centered roughly
on Monday, and a second sometime Tuesday or Wednesday. Between these
peaks, the moisture feed is unlikely to shut down completely,
leading to a long-duration event rather than two isolated episodes.

Ensemble IVT guidance continues to show a broad range but retains a
strong signal for an impactful event. For the first  plume on
Monday, GEFS and ECMWF are similar, with members clustering around
600-650 kg/ms and higher-end solutions near 750-800 kg/ms. The
second surge maintains mean values in the 500-600 kg/ms range with
high-end members closer to 750-850 kg/ms. The precise timing and
latitude of these plumes remain uncertain, but confidence continues
to increase that the region will experience a prolonged period of
moderate to heavy rainfall. Winds early next week may also trend
breezy, but ensemble spread remains wide. Even moderate gusts in a
30-40 mph range could be sufficient to bring down isolated trees due
to increasingly saturated soils. This remains a detail to refine as
the event draws closer.

Overall, the Monday-Wednesday period remains the primary focus for
potential high-impact hydrologic (see hydrology section below for
more details) and wind concerns. Confidence in a multi-day
atmospheric river is rising, but exact rainfall totals and timing
details still require several more forecast cycles to resolve. While
rain is looking to continue through at least Thursday, rain amounts
look much less Thursday and onward.
~12

&&

.HYDROLOGY...A series of frontal systems will keep conditions
wet through the weekend and much of next week. The most notable
period will be late Monday through late Wednesday, where a
prolonged atmospheric river may bring significant rainfall and
rising rivers across southwest Washington and northwest Oregon.
Rivers draining the Coast Range and Willapa Hills have a 10-25%
chance of reaching moderate flood stage and a 8-15% chance of
reaching major flood stage. There is also the potential for
flooding along small creeks and streams, as well as urban
flooding. Flooding of the Willamette mainstem rivers is unlikely
to occur (less than 10%). Probabilities for specific river
points can be found at the National Water Prediction Service
website. Periods of heavy rain will also increase the risk for
landslides in areas of steep terrain, and debris flows over
recently burned areas.

&&

.AVIATION...Radar imagery and terminal observations as of late
Friday morning depict a mix of IFR/low-end MVFR CIGs and VIS across
all terminals as a warm front lifts over the region and brings rain
and mist. Moderate to heavy rain at times are bringing brief
reductions in VIS to 2-4 SM. Expect this trend to continue through
this morning and early afternoon. After 21z Fri-00z Sat, rain will
decrease and transition to post-frontal showers. Visibility should
trend back up to VFR thresholds and CIGs should begin to lift toward
high-end MVFR/low-end VFR. Expect west-southwesterly winds today
across all terminals, around 10-15 kt with gusts up to 25 kt along
the coast and 20 kt across the Willamette Valley. Winds will
gradually weaken overnight as the system exits the area.

KPDX AND APPROACHES...Low-end MVFR CIGs continue through the early
afternoon with the warm front passage. Moderate to heavy rain at
times may bring brief VIS reductions to 3-5 SM. After 21z Fri, rain
becomes light and transitions into showers. CIGs will then trend
toward high-end MVFR (above 2000 ft). Southwesterly winds 10-13 kt
with gusts up to 20 kt today, weakening below 10 kt tonight.    -10

&&

.MARINE...A frontal system will move over the waters today, with
westerly winds increase to 15 to 25 kt with gusts up to 30 kt,
strongest over the northern waters. Small Craft Advisories remain in
effect across all waters including the Columbia River Bar beginning
4 AM Friday, lasting through Saturday evening. Seas of 4-5 ft early
this morning will build to around 7-9 ft at 10-11 seconds by Friday
evening as a northwesterly swell moves in with the next system. Will
note that a very strong ebb may lead to higher seas of 10-11 ft in
the Main Channel of the Columbia River Bar around 4-5 PM Friday. For
the rest of the waters, seas likely (80% chance) build above 10 ft
by late Saturday morning. There is also a 25% chance that seas build
above 13 ft, with the highest chances north of Cape Lookout and
beyond 10 NM. There is a 1-5% chance seas peak as high as 15 ft.

The parade of fronts continue through the weekend and into early
next week. Chances for widespread and frequent Gale force wind gusts
of 34 kt or greater remain under 15% through early next week;
however, chances for brief and isolated Gale force wind gusts are
around 40-50% on Sunday and 50-70% on Monday. Seas are forecast to
hover close to 15 ft from late Monday through late Wednesday, with a
10% chance seas peak around 17-18 ft.      -10/23

&&

.BEACH HAZARDS...Coastal Flood Advisories remain in effect from
for minor tidal overflow during high tide from 9 AM to 3 PM Friday
and Saturday for the south Washington coast and Clatsop County coast
 in Oregon. Minor flooding up to 1 foot above ground level is
possible during high tide in low lying areas near bays, sloughs, and
the low reaches of the coastal rivers. Coastal residents in the
warned area should remain alert for rising water and take
appropriate action to protect life and property.      -10

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Coastal Flood Advisory from 9 AM this morning to 3 PM PST this
     afternoon for ORZ101.

     Coastal Flood Advisory from 9 AM to 3 PM PST Saturday for ORZ101.

WA...Coastal Flood Advisory from 9 AM this morning to 3 PM PST this
     afternoon for WAZ201.

     Coastal Flood Advisory from 9 AM to 3 PM PST Saturday for WAZ201.

PZ...Small Craft Advisory until 10 PM PST Saturday for PZZ210-251>253-
     271>273.
&&

$$

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