723
FXUS66 KPQR 132215
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
215 PM PST Sat Dec 13 2025

.SYNOPSIS...High pressure will maintain dry weather across NW Oregon
and SW Washington through tonight. On Sunday, a weak front will move
over the area bringing another round of light rain. A pair of quick
moving frontal systems associated with subtropical moisture will
bring additional rounds of heavier rainfall and river rises, though
probabilities for exceeding minor flood stage at the majority of
rivers remains around 20-25% or less. Breezy to gusty southerly
winds are also expected with the strongest winds likely Tuesday
night. Onshore flow continues with showers on Wednesday. Lowering
snow levels will allow for snow to fall at pass level in the
Cascades. Precipitation continues through late next week, with
potential for another strong system on Thursday.

&&

.DISCUSSION...Tonight through Friday...Water vapor satellite imagery
this afternoon reveals an upper level ridge situated over the
Pacific Northwest, with the main ridge axis shifting east of the
Cascades. Visible satellite imagery shows widespread stratus through
much of the Willamette Valley, but showing indications of scattering
out, especially along the fringes with skies becoming mostly sunny
this afternoon. There is a chance some areas in the central valley
may remain socked in throughout the day. With the surface inversion
in place, also seeing warmer temperatures into the mid-60s at higher
elevations in the Coast Range and foothills of the Cascades. Good
day for a hike!

Increasing clouds by Sunday as a weak front approaches the coast
early Sunday morning. The upper shortwave trough quickly lifts north
into British Columbia, removing much of the synoptic support for
this system, and allowing for the front to decay and dissipate as it
pushes inland. Rainfall amounts are not expected to be overly
impressive on Sunday, with most likely amounts ranging from 0.1-0.4
inch along the coast and Coast Range, while amounts will likely
range from a trace up to a quarter inch inland, highest amounts in
southwest WA and lowest to the south.

More active weather looks to return by Monday, and continue through
much of next week. A broad upper level trough will persist over the
Pacific as strong low pressure systems spin in the Gulf of Alaska
through late next week. A strong jet stream, associated with
subtropical moisture at times is expected to be directed toward the
Pacific NW during this time. The first system next week will be
associated with IVT values peaking around 750-1000 kg/m/s, which
would place it in the strong atmospheric river category. But, what
makes this different from last week`s AR event is both a shorter
duration and a more southwest orientated flow. Ensembles are
suggesting the initial surge of moisture Sunday night into Monday
morning likely remains north over Washington, before the front
quickly pushes through NW Oregon, followed by more showery
conditions by Monday afternoon. Most likely rainfall totals in
coordination with the WPC through Monday evening has decreased
somewhat: around 0.25-0.75 inch within the interior lowlands, and
from 0.75 up to 2 inches along the coast and Coast Range, and
potentially up to 2.5 inches in 24 hours within the Cascades. The
highest probabilities (50-70%) for exceeding 2 inches of rainfall are
in the higher terrain of SW Washington and the northern Oregon Coast
Range, but chances of exceeding 4 inches is less than 10%. The main
concern with this pattern remains on rivers that are running high
from last week`s rainfall.

Another concern with this first system on Monday will be potential
impacts from winds. South to southwesterly winds will likely
increase ahead of the system late Sunday night into Monday morning.
Wind gusts are most likely to peak along the coast around 40-50 mph
and inland around 25-35 mph, though there is around a 10-20% chance
of wind gusts exceeding 40 mph through the Willamette Valley. The
combination of saturated soils and the strongest wind gusts could
produce isolated downed trees and power outages.

The rain is still expected to ease, with scattered showers likely
through Tuesday morning. But, the next frontal system arrives later
Tuesday, bringing another round of rain and wind. Again, this
frontal system appears to move fairly quickly across the area
Tuesday night. While IVT values are modeled to be slightly lower,
potentially peaking around 500-750 kg/m/s (moderate AR category),
total rainfall amounts are likely to be similar to Monday`s system.
Models and their ensembles are indicating this system may be more
dynamically driven as a stronger shortwave trough and associated
vort max slide across the region. This also signals to potential for
stronger, and perhaps more impactful winds across the area Tuesday
night. Probabilities for wind gusts exceeding 40 mph have increased
to around 50-60% through the southern and central Willamette Valley.

Snow levels are expected to drop significantly by Wednesday morning
with the passage of the upper trough. This will allow for snow to
begin accumulating at pass level on Wednesday. The weather setup on
Wednesday will feature onshore flow with zonal flow aloft, likely
maintaining showers enhanced by orographic effects. There remains
quite a large spread of uncertainty for snowfall amounts through
Wednesday night, though probabilities for exceeding 6 inches is
around 50%, and 10-30% for exceeding 12 inches in 24 hours. (The
NBM`s 10th and 90th percentiles at Santiam Pass are currently
sitting at 1 inch to 20 inches!) So, if you plan on traveling across
any of the Cascades passes next week, keep an eye on updated
forecasts.

As the synoptic pattern progresses into late next week, uncertainty
also remains fairly high. The GEFS and ECMWF ensembles, which were
quite different just 24-hour ago, have come closer together, but the
individual members remain wildly separated. It is likely (>90-95%
chance) the rain will continue Thursday and Friday, but rainfall
amounts are quite uncertain. That said, a stronger atmospheric river
appears likely to set up somewhere along the west coast late next
week, with the highest probabilities farther south near the Oregon-
California border. But if that were to shift north, we could see
much higher rainfall amounts impacting our forecast area.

&&

.AVIATION...Latest satellite imagery continues to highlight valley
fog and low stratus, with largely IFR cigs but unrestricted vis
at central and southern Willamette Valley terminals. To the north
in the northern Willamette Valley, Portland-area, and inland
along the Lower Columbia/Cowlitz Valleys, skies have mostly
cleared. Increasing diurnal mixing will continue to improve
conditions with prevailing VFR favored across the region by
21-24z Sat, however there remains a 30-40% chance that MVFR or
worse stratus will persist generally from KSLE to the south.
Along the coast, light offshore winds have maintained clear skies
with VFR expected to continue through much of the period, while
winds increase out of the south with gusts to 20 kt.

Continued clear skies ahead of a frontal system approaching the
region early Sunday morning may allow for additional radiation fog
to develop tonight, particularly if low clouds and rain showers
along the front are delayed. More likely, MVFR cigs with light
rain will arrive from the northwest by 09-15z Sun for most.

KPDX AND APPROACHES...Remaining low cloud cover continues to
erode as diurnal mixing increases, with VFR conditions favored
through at least 09-12z Sun. Largely southeast winds at around 5
kt expected through the period. Light rain showers and MVFR cigs
along a front may arrive by 12z Sun. -36

&&

.MARINE...A ridge of high pressure shifting eastward away from the
region through tonight will see tranquil conditions today give way
to rain showers and increasing southerly winds on Sunday as a
weak front tracks over the waters. Small Craft Advisories remain
in effect from tonight through Sunday evening for wind gusts of
20-25 kt while seas rise to 7-10 ft.

A stronger system looks to affect the coastal waters on Monday.
Ahead of a strong cold front, a tight pressure gradient will favor
widespread southerly gales from late Sunday evening through Monday
afternoon while a building west-southwesterly swell will see seas
rise above 15 ft by Monday morning. While there is high confidence
in gales, and a Gale Warning is now in effect from Sunday night
through Monday afternoon, there remains a 25-45% chance in at
least isolated storm-force gusts around 50 kt Monday morning
across the inner waters, and 5-25% chance across the outer waters.
Meanwhile, seas most likely build to 16-18 ft by Monday afternoon.
Chances for seas above 15 ft are high, 65-95%, beyond 10 NM and
north of Cascade Head, and less so to the south and east. Chances
seas reach 18 ft or greater are only 15-35% beyond 30 NM north of
Cape Falcon, and less than 10% elsewhere.

The weather pattern then looks to remain very active through the
middle and latter portions of next week. Seas are very likely to
remain elevated above 10 ft (greater than 90% confidence), and
possibly (50% chance or higher) above 15 ft on Wednesday and
Thursday as another potent weather system moves onshore. -36

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 10 PM this evening to 1 AM PST Monday
     for PZZ210-253-273.

     Gale Warning from 1 AM to 4 PM PST Monday for PZZ210-253-273.

     Small Craft Advisory from 7 PM this evening to 10 PM PST Sunday
     for PZZ251-252-271-272.

     Gale Warning from 10 PM Sunday to 4 PM PST Monday for PZZ251-252-
     271-272.

&&

$$

www.weather.gov/portland

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