087
FXUS66 KPQR 161812
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1012 AM PST Sun Nov 16 2025

.UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...Rain returns by this evening as the progressive and
active pattern continues. Through the workweek, repeated
systems will bring cooler temperatures along with multiple
chances for lowland rain and mountain snow to the region.

&&

.SHORT TERM...Now through Tuesday Night...Sunday will feature a
dry start but with a foggy morning for many lowland locales.
Moist low levels beneath largely clear skies has resulted in
ample radiation fog developing early this morning. Observed
visibilities along the coast and through the northern
Willamette, Lower Columbia, and Cowlitz Valleys have sunk below
1 mile, while latest satellite imagery depicts fog or low
stratus clouds also affecting Coast Range Valleys. While the
central and southern Willamette Valley has generally maintained
higher visibility beneath low stratus thus far into the
overnight period, conditions could still support fog development
before sunrise. Areas of dense fog and visibilities below 1/4
mile are most likely in typical fog- prone areas including
sheltered valleys or low spots within larger valleys, as well as
areas near rivers or other water sources. Visibility will
likely improve as diurnal mixing increases in the hours
following sunrise, however additional cloud cover associated
with an approaching frontal system will make it difficult to see
any substantial clearing of low clouds today.

A narrow and elongated upper-level trough over the Northeast
Pacific will swing into the coast this evening as a surface cold
front traverses the region through tonight. Precipitation will
most likely begin by 9-10 AM along the coast, by noon along the
I-5 corridor, and by 2-3 PM in the Cascades. At the earliest,
rain could begin about two hours earlier while at the latest,
its onset could be delayed about two hours later. With snow
levels remaining above 6500 ft through tonight, precipitation
will largely fall as rain in the Cascades aside from the highest
peaks. As the trough moves inland, its base pinches off to form
a cutoff low over California while the remaining rump trough
lifts into southern British Columbia, leaving much of the region
displaced from the best forcing for ascent and therefore
lowering potential rainfall amounts compared to areas to the
north and south. Through tonight, most likely rainfall amounts
remain around 0.3-0.5" along the I-5 corridor and 0.5-1" along
the coast and in higher terrain. In the wettest scenario where
the trough maintains its structure as it moves inland, about a
10% chance of occurrence, higher rainfall totals of 0.5-0.75"
could be observed along the I-5 corridor and 0.75-1.5" along the
coast and in higher terrain.

While the developing split flow pattern will see coverage of
showers decrease through Monday and Tuesday, much cooler air
moving in overhead will see snow levels fall to 3500-4500 ft by
Tuesday morning. By this time, precipitation amounts will be
much lower, so while snow may fall down to Cascade pass-level,
impactful accumulations are not anticipated. Cooler air aloft
will be reflected in surface temperatures with highs likely only
reaching the low to mid 50s for valley areas on Tuesday. Tuesday
night may be the coldest of the season so far for many with lows
expected to fall into the mid to upper 30s for most. -36


.LONG TERM...Wednesday through Saturday...The active pattern
continues through the latter half of the week as another trough
looks to move inland late Wednesday into Thursday, however there
remains significant uncertainty in its evolution, particularly
whether it will follow a similar pattern of splitting into a
cutoff low to the south, thereby leaving northwestern Oregon
and southwestern Washington in a region of weak forcing and
successive forecasts of lower precipitation amounts. As before,
in the scenario of a more coherent trough affecting the region,
the combination of cool air aloft and ample moisture could
support impactful snow accumulations down to pass-level in the
Cascades, although this is an unlikely solution at this point.
Chances for 6 inches of snow Thursday through Friday at the
Cascade passes is a mere 5%. Otherwise, seasonable temperatures
with persistent 25-50% chances of rain showers are favored
across the region through the workweek. Long-range guidance
features low probabilities of another impactful system by next
weekend. -36


&&

.AVIATION...Currently, observations show largely IFR conditions
across the region this morning with localized pockets LIFR for
spots like the Tualatin Valley. However CIGs/VIS have been
slowly trending higher over the last hour or two, and with the
arrival of the cold frontal boundary late this morning into the
afternoon inland terminals likely see conditions improve to
low-end MVFR. This transition should closely match the arrival
and increase of light rainfall around 19-21z today. Winds
currently out of the south-southeast late this morning will
shift out of the northwest at 5-15 kt behind the boundary
~00-06z Mon. The continuation of MVFR to IFR CIGs/VIS are
favored the latter half of tonight into Monday morning.

KPDX AND APPROACHES...Current IFR conditions are expected to
improve back to MVFR over the next few hours (~19-21z) as a cold
front arrives from the west bringing some added mixing but also
light rainfall. However, confidence is moderate to high (50-70%)
for the return of IFR CIGs later this evening and overnight
starting around ~06z and continuing through much of Monday
morning. South winds around 5-10 kt turn out of the northwest
behind the aforementioned frontal boundary. -99

&&

.MARINE...Seas of 7-9 ft at 13 seconds continue across the
waters, but will build to 9-11 ft by this afternoon and further
to 12-15 ft by Monday morning as a frontal system tracks across
the region. A Small Craft Advisory therefore remains in effect
as seas remain elevated through Monday evening. Another frontal
system will traverse the waters Sunday evening into Monday, with
initial southwest winds becoming northwesterly with gusts up to
25 kt behind the boundary, mainly for the outer waters. A
building westerly swell will cause seas to rise to 12-15 ft by
late Sunday night or Monday morning, before falling below 10 ft
early Tuesday morning. Wednesday into Thursday, yet another
system will see increasing winds and building seas across all
waters. The robust swell expected mid to late this week has a
high probability of exceeding 15 ft, but there is also a 25%
chance of 20 ft seas and a 10% chance of 22 ft seas or higher.
-42/36

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 7 PM PST Monday for PZZ210.
     Small Craft Advisory until 10 PM PST Monday for PZZ251>253-
     271>273.
&&

$$

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