879
FXUS66 KPQR 170958
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
258 AM PDT Fri Oct 17 2025

.SYNOPSIS...Transient shortwave ridging Friday night will bring
chilly overnight temperatures and areas of frost for some inland
valleys. A robust frontal system arrives late Saturday into Sunday,
bringing widespread soaking rain to the area with gusty southerly
winds. Trending drier Sunday night into early next week, however some
uncertainty remains with a 20-45% chance of rain returning by
Wednesday.

&&

.SHORT TERM...Now through Sunday Night...Satellite, radar and surface
weather observations from early Friday morning depicted a decaying
cool front draped over far northwest Washington, extending
southwestward into the coastal waters. This front should continue
weakening as it slowly sags southward into southwest Washington and
northwest Oregon, resulting in very little to no measurable rainfall
for most locations. The main exception will be in the south
Washington Cascades/foothills and along the south Washington/north
Oregon coast. These areas have an 80-90% chance for at least 0.05" of
rain.

Transient ridging builds into the area this afternoon into early
Saturday, setting the stage for clear skies and calm winds. This will
lead to chilly temperatures once again for inland valleys
Friday night into Saturday morning. The coldest areas will likely be
the Upper Hood River Valley, south WA Cascade foothills, Battle
Ground and Ridgefield areas. Confidence is generally over 70-80%
these zones will see low temperatures dip to 33-36 degrees, which has
prompted the issuance of Frost Advisories Friday night into Saturday
morning. Meanwhile, a Freeze Warning is in effect for the Upper Hood
River Valley for low temperatures as cold as 29-30 degrees. While
frost is also possible in portions of the southern Willamette Valley,
especially east of I-5, confidence is currently not high enough to
include these zones in the Frost Advisory. This is due to potential
low clouds or fog that may develop instead of frost; the HREF
currently shows a 50-75% chance for low cloud development mid to late
Friday night, which would favor temps bottoming out in the upper 30s
with minimal frost concerns. The overall weather pattern beyond
Friday morning does not favor widespread frost or freeze concerns, so
this round of frost/freeze headlines may wind up being the last of
this growing season.

Despite the chilly temperatures in place Saturday morning,
temperatures will rebound nicely in the afternoon with highs in the
60s, except near 70 degrees in Eugene-Springfield, Creswell, Blue
River, Lowell and Oakridge. These areas will see sunny skies
throughout the day, however northern areas will see clouds begin to
increase ahead of the next frontal system. Models are in good
agreement on the timing of this front, bringing stratiform rain to
southwest Washington and the north Oregon coast Saturday evening and
then the rest of northwest Oregon from Lane County northward Saturday
night into Sunday morning. Persistent stratiform rain will transition
to post-frontal showers by late Sunday morning or early Sunday
afternoon. This is when forecast soundings show 850 mb temperatures
cooling to +1 to +2 degrees Celsius, with SBCAPE values increasing
to 100-200 J/kg and equilibrium levels generally below -10 degrees
Celsius. However, 0-3 km AGL bulk shear values are fairly high at
30-35 kt (have opted to use 0-3 km AGL bulk shear values instead of
0-6 km as cloud tops generally look to stay near or below 3 km). Both
speed shear and directional shear are in place, as the wind direction
will veer with height for a few hours or so as the upper level trough
axis moves overhead. The limited instability and shallow nature of
Sunday`s convection suggests overall lightning activity will most
likely be limited (which helps explain why NBM thunder probabilities
only peak around 10-15%). However, whether lightning occurs or not,
stronger showers will have the potential to produce a funnel cloud,
landspout, or gusty outflow winds up to 45 mph given the
environmental wind profile in place, meaning highly localized wind
damage is possible. Note southerly winds will be breezy in general
Saturday night and Sunday, even away from showers and thunderstorms.
Currently expecting southerly wind gusts up to 20-30 mph for inland
areas and up to 30-40 mph for the south WA/north OR coast. Gusts up
to 40-50 mph appear likely in the high Cascades. Winds will weaken
Sunday night while any lingering showers begin to dissipate. -23


.LONG TERM...Monday through next Friday...Most model guidance
suggests dry weather with seasonable temperatures, relatively light
winds and a mix of clouds and sun Monday and Tuesday. That said,
there remains a handful of GEFS/ENS ensemble members with light QPF
amounts Monday morning/afternoon and Tuesday morning/afternoon as a
pair of weak upper level impulses move overhead. As such, there is a
10-30% chance of light rain showers on Monday and 15-35% chance on
Tuesday. Probabilities are highest along the south WA/north OR coast.

Chances for rain gradually increase late Wednesday through Thursday
night, peaking near 75-85% by early Friday morning. This system has
the potential to bring more impactful rain amounts and gusty south
winds, however uncertainty is high in regards to exact rain amounts
and exact wind speeds, as the outcome will be highly dependent on the
exact track and strength of a negatively tilted trough and associated
deepening surface low that will be moving somewhere over the coastal
waters during that time. Ensemble low locations vary significantly
both spatially and temporally, with some ensemble guidance suggesting
a fairly weak low with minimal impacts, while other members suggest a
very strong low capable of wind damage somewhere along the
Washington, Oregon, or northern California coast. There is currently
a 15-25% chance for max wind gusts of 45 mph or stronger across all
of northwest Oregon and southwest Washington, except for a 35-50%
chance at the coast and on exposed ridges in the Coast Range and
Cascades. This system will also bring a 40-80% chance of 1" of rain
or more, with the lowest probabilities in the Portland metro and
Willamette Valley west of the I-5 corridor and the highest
probabilities in the mountains and at the coast. -23

&&

.AVIATION...A weak cool front will continue sagging southward over
southwest WA and far northwest OR this morning, bringing MVFR cigs
to the coast. MVFR cigs have already developed at KAST, and should
spread southward down to KONP around 12-14Z Friday as the front
progresses. It appears inland areas will remain VFR through 12-15z
Friday before a brief period of MVFR cigs between 15-18z Friday
as the front decays overhead. There is a 60-80% chance for cigs
below 3000 ft at all inland terminals, except 30-40% at KEUG).
Winds will remain light and variable around 5 kt or less at all
TAF sites through 12z Saturday.

KPDX AND APPROACHES...VFR CIGs through the TAF period, with cigs
likely lowering to around 2800-3000 ft after 12-15z Fri with a
weak frontal passage (75% chance for cigs at or below 3000 ft).
Light and variable winds under 5 kt continue. -23

&&

.MARINE...Winds return to a northerly direction behind a weak
frontal passage Friday morning around 10-15 kt as high pressure
rebuilds. Seas hold around 4-6 ft at 14-15 seconds. Conditions
become more active on Friday evening as a northwesterly swell
enters the waters due to a low pressure system over the Gulf of
Alaska. This swell will build seas to 11-13 ft at 14-16 seconds,
resulting in hazardous conditions for small craft. Small Craft
Advisories go into effect across all waters including the Columbia
River Bar 5 PM Friday and last through at least Saturday evening.
Winds will stay rather tame out of the north with gusts up to
10-15 kt into Saturday morning.

The weather pattern remains active Saturday night into early next
week as a stronger frontal system progresses through the waters
and brings breezy southerly to westerly winds. Marine conditions
quickly amplify as a higher northwesterly swell enters the waters,
building seas above 15 ft at 15 seconds (>90% chance) on Sunday.
Chances for seas above 20 ft have decreased and are now near 0%,
indicating increasing confidence is the wave height forecast. In
addition to increasing seas, winds will likely gust up to 25-30
kt. Brief and isolated gale forced wind gusts up to 35 kt are
possible over the northern inner waters with the frontal passage
Saturday night into early Sunday morning, including the main
channel of the Columbia River Bar.

Seas will decrease later Monday into Tuesday morning, bottoming
out around 8-10 ft at 13 seconds before another potent
northwesterly swell arrives Tuesday afternoon and evening pushing
seas into the 10-15 ft range again. -23/10/99

&&

.BEACH HAZARDS...A northwest swell of 10-12 ft at 15 to 18 seconds
seconds is expected to enter the waters Friday evening. This
increase in wave energy will support a high threat for sneaker
waves through this weekend. A Beach Hazards Statement remains in
effect across the Central and Northern Coast of Oregon and the
South Washington Coast, which is now in effect through Sunday
evening. Sneaker waves can run up significantly farther on a
beach than normal, including over rocks, logs, and jetties.
Sneaker waves can suddenly knock people off of their feet and
quickly pull them into the ocean which may lead to serious injury
or drowning. Caution should be used when in or near the water.
Always keep an eye on the waves, and be especially watchful of
children and pets. Remember, never turn your back on the ocean!
-23/10/99

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Frost Advisory from midnight tonight to 9 AM PDT Saturday for
     ORZ104.

     Freeze Warning from midnight tonight to 9 AM PDT Saturday for
     ORZ121.

WA...Frost Advisory from midnight tonight to 9 AM PDT Saturday for
     WAZ205-208.

PZ...Small Craft Advisory from 5 PM this afternoon to 2 PM PDT
     Saturday for PZZ210.

     Small Craft Advisory from 5 PM this afternoon to 8 PM PDT
     Saturday for PZZ251>253-271>273.
&&

$$

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