721
FXUS66 KPQR 252303
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
303 PM PST Tue Nov 25 2025

.SYNOPSIS...The arrival of a warm-frontal system this afternoon
kicks off a fairly wet stretch of weather for NW Oregon and SW
Washington through Thursday. At least snow-levels climbing to
6,000-8,500 feet will help to mitigate any significant travel
concerns across the Cascade Passes. Conditions gradually trend
drier Friday into Saturday with lingering precipitation largely
pinned to higher terrain features - snow levels drop to the
passes by late Friday and Saturday. Looking ahead, guidance
continues to show a cooling trend taking hold by early next
week, however, beyond the potential for our coldest low
temperatures of the season additional impacts appear minimal
through Tuesday at this time.

&&

.DISCUSSION...Now through Tuesday...This afternoon a warm
frontal system has taken aim at the region by steering a stream
of atmospheric moisture into western Oregon and Southwest
Washington. Currently surface observations show above freezing
temperatures across the the Cascades passes helping to keep
travel impacts largely in check before snow levels have a
chance to jump to 6,000-8,000 ft later this evening - highest
relative snow levels south near Willamette pass. As we progress
through tonight, this elongated band of rainfall oriented WSW to
ENE is expected to slowly shift southward with the majority of
deterministic and ensemble guidance depicting the axis of
heaviest rainfall south of the Portland/Vancouver metro by
sunrise Wednesday. That said, moisture begins to slowly creep
northward through the day Wednesday into Wednesday evening
thanks to a developing secondary low pressure system over the
eastern Pacific. Between high resolution guidance and global
models there is still some lingering uncertainty as to just how
quickly this S to N transition takes place - if precipitation
stalls and get hung up over a section of Western Oregon and
Southwest Washington longer than anticipated some of the more
responsive rivers, primarily in the coast range and Willapa
Hills, may be more impacted. However, the chances for minor
river flooding appear low (<15%) at this time. Confidence in the
QPF forecast through Wednesday night is only moderate due to
this previously mentioned uncertainty.

Turning our attention to the developing low pressure system off
the coast Wednesday night into Thursday, the latest 12z
ensemble runs for the EPS, GEFS, and GEPS (including their
deterministic counterparts) have continued project the core of
the low moving into Washington/Oregon coastline. There`s a bit
of N to S variability on where exactly where along the coast
the low will move inland, but the majority of the ensemble
members suggest this will be somewhere between central
Washington and northern Oregon. This is further south when
compared to yesterdays 12z model runs in addition to a slight
delay in arrival time. Ultimately, there`s not much change in
the overall impacts with this system except for potentially
slightly increased winds depending on exactly where the low sets
up. Current probability for 30+ mph winds are 10-25% for
interior lowlands and 50-70% along the coast, mainly Astoria
southward. Probability for 40+ mph winds drop to less than 5%
across the interior lowlands and 25-30% along the coast. Rain
amounts for a localized area will likely fluctuate based on the
exact low track too, but not expecting a significant amount of
rain on top of accumulation from the preceding warm-frontal
system overhead. From Thursday through Thursday night expect
another 0.15-0.25 inch for the central and southern Willamette
Valley, 0.3-0.75 inch for the northern Willamette Valley into
the SW Washington lowlands, 0.5-1.25 inches along the coast and
Coast Range, and 0.5-2 inches along the Cascades (highest SW
WA).

Then Friday into the weekend and beyond, model uncertainty
increases further as both deterministic and ensemble systems
struggle to resolve the placement of the upper-level longwave
pattern across the eastern Pacific and western CONUS. On
Saturday in particular guidance is split as to whether another
shortwave trough near British Columbia dives southward into the
Pacific Northwest, or if high pressure ridge over the eastern
Pacific strengthens enough to keep this feature well to our
east. As of 12z, around 65-70% of GEFS/EPS ensemble members, and
the ECMWF AIFS favor a drier solution Saturday while the other
30-35% of ensemble members and deterministic ECMWF would
facilitate a period of shower activity which would almost
certainly bring light snowfall to the passes. At the very least
all models solutions do show the development of broad northerly
flow which favors a cooling trend into Sunday and Monday,
although the vast majority of guidance (80%+) now keep the
coldest airmass near the Rockies. The NBM probabilities for
subfreezing low temperatures across the lowlands are still
rather good, generally 45-75%, by Monday morning which will give
us a shot for the lowest temperatures of the season thus far.
Come Tuesday models do hint at a potential shortwave sliding
south-southeastward into the Pacific Northwest which would
increase showery precipitation chances again. All in all, the
overall model spread is moderate to large during this early
next week period with impacts beyond a decrease in temperatures
staying near climatological norms for late November/early
December. Still, it`ll be worth keep an eye on the forecast as
we go through this week, especially if you have holiday travel
plans.  -99/03

&&

.AVIATION...At 22z Tuesday, widespread light stratiform rain was
being observed across all of southwest WA and northwest OR. Cigs
were mainly in the VFR range above 5000 ft, however surface
visibilities were beginning to lower to around 4 SM is southwest
WA and at KHIO where rain is becoming slightly heavier. Expect
surface visibilities to lower to 3-6 SM at all terminals later
Tuesday evening as rain becomes slightly heavier from north to
south.

In addition to lowering surface visibilities, cigs will gradually
lower between 03-12z Wednesday from north to south, with
probabilities for cigs below 3000 ft increasing to 70-90% and
probabilities for cigs below 1000 ft increasing to 10-30%, except
90% at the coast where IFR cigs are very likely to occur. Overall,
inland terminals will trend towards predominately MVFR while
coastal terminals trend towards predominately IFR. Expect very
little improvement through the day on Wednesday as widespread
stratiform rain continues and cigs hold fairly steady.

KPDX AND APPROACHES...VFR cigs/visibilities will likely continue
through at least 00z Wednesday before cigs lower to MVFR
thresholds or lower Wednesday evening as rain becomes slightly
heavier. Probabilities for cigs below 3000 ft rapidly increase to
80% at 03z Wednesday. Probabilities for cigs below 1000 ft
increase to 30% at that time as well. Once cigs fall to IFR or
MVFR thresholds, expect very little to no improvement through 00z
Wednesday as persistent stratiform rain continues. -23

&&

.MARINE...South winds up to around 30 kt will continue through
Tuesday evening ahead of a cold front that will move over the
coastal waters Tuesday night. Seas will rise to 9-11 ft at 12
seconds by Tuesday night, continuing through early Wednesday
morning before falling to around 7-8 ft after sunrise. A Small Craft
Advisory remains in effect through 4 AM Wednesday for all marine
zones, except through 1 AM Wednesday for the Columbia River Bar,
to cover the gusty southerly winds through Tuesday evening and for
the period of steeper seas to follow.

Another frontal system approaches the waters sometime Wednesday
night into Thursday, though there are still uncertainties in exact
timing. Another round of increased southerly wind gusts up to at
least 30 kt is expected with this system. There`s a 45-60% chance
for maximum wind gusts to peak around 35 kt for all marine zones,
though 3 hourly probabilities drop to 10-20%, indicating
widespread gale force wind gusts are unlikely to occur. Seas will
most likely peak near 14-16 ft late Thursday with a 5-10% chance
seas peak as high as 20 ft. This is due to the uncertainty regarding
the exact strength and track of the closed surface low and the
frontal system accompanying the low. Regardless of the outcome
for this system, winds and seas will lower significantly on
Friday. Winds and seas over the upcoming weekend are currently
forecast to stay below small craft advisory thresholds with a
period of offshore flow. -23/03

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 1 AM PST Wednesday for PZZ210.
     Small Craft Advisory until 4 AM PST Wednesday for PZZ251-252-
     271>273.
     Small Craft Advisory until 4 AM PST Wednesday for PZZ253.
&&

$$

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