Thurston, Oregon Weather Forecast Discussion

928
FXUS66 KPQR 121834 AAA
AFDPQR
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1134 AM PDT Fri Sep 12 2025
Updated aviation discussion.
&&
.SYNOPSIS...Widespread stratus across northwest Oregon and
southwest Washington this morning should break out to sunny
skies this afternoon as high pressure builds. Warm and dry
conditions continue through tomorrow afternoon. Our next frontal
system arrives Saturday night to Sunday, bringing widespread,
light rain showers. Conditions dry and warm up again early next
week with the potential for light offshore winds Monday and
Tuesday nights.
&&
.SHORT TERM...Now through Sunday Night...Satellite imagery and
surface observations as of early Friday morning depicts
widespread stratus across northwest Oregon and southwest
Washington as the low-level atmosphere remains moist with light
and variable winds. Stratus didn`t completely clear out
yesterday, however, there is high confidence that clouds will
clear out this afternoon since an upper level shortwave ridge
will begin to move overhead. Conditions will warm and dry up as
high pressure builds today, so we should see a sunny afternoon.
Expect seasonable temperatures with afternoon highs in the mid
to upper 70s across interior valleys and mid to upper 60s along
the coast.
Tonight, increasing high pressure will favor a lower-level
marine layer along the coast and potentially lead to fog and
thus visibility reductions. Model soundings suggest that low
stratus also re-develops across the Willamette Valley and
southwest Washington lowlands tonight as the surface moistens
under the nighttime inversion. High pressure with sunny skies
continues through Saturday afternoon, with temps warming
slightly into the low 80s across interior valleys. By Saturday
evening, the aforementioned shortwave ridge will progress
eastward with increasing cloud cover across the area as the next
frontal system approaches.
Cooler temperatures and widespread rain showers return Saturday
night into Sunday across northwest Oregon and southwest
Washington as our first fall-like frontal system swings through
the region. Forecast rain totals in a 24 hour period from 11 PM
Saturday to 11 PM Sunday amounts are around 0.10-0.30" across
most interior valleys (except 0.05" or less in the Upper Hood
River Valley), 0.20-0.40" along the coast, and 0.30-0.60" across
the Coast Range, Willapa Hills, and Cascades (highest amounts
forecast on the west slopes of these mountains). Afternoon highs
are forecast to cool down to the low 70s across interior
valleys.
Higher rainfall amounts can`t be ruled out if the front comes
in stronger. NBM chances for 24 hour rain totals of 0.50" or
greater ending 11 PM Sunday are 40-50% across the Willamette
Valley and southwest Washington lowlands. For 1" or greater
along the coast during this same timeframe, those chances are
30-50% (highest chances from Lincoln City northward). Will also
note that there is a 10-20% chance for post-frontal
thunderstorms Sunday afternoon behind the front. As the upper
atmosphere cools with this system, this would support increasing
instability and thus the potential for thunderstorms. Any
passing thunderstorms may result in lightning and brief heavy
rain. By Sunday evening, the front further weakens and exits
the area, resulting in rain showers gradually tapering off
Sunday night into early Monday morning.       -Alviz
.LONG TERM...Monday through Thursday...Shortwave ridging
returns on Monday as the previous frontal system progresses
eastward. This will return dry conditions and clearing skies by
Monday afternoon. Tuesday, there is high agreement among
ensemble members in a return to above-average 500 mb heights as
the ridge axis centers over the Pacific Northwest. This would
maintain sunny skies and lead to temperatures rebounding into
the mid 80s across interior valleys.
It`s worth highlighting late Monday night and Tuesday night, a
thermal trough develops across western Oregon with high pressure
east of the Cascades, leading to an offshore flow pattern.
There remains some uncertainty in the exact placement and
magnitude of this feature which would determine the strength of
offshore winds, but for now they don`t appear particularly
strong. This will be a period to monitor in the coming days.
Wednesday to Thursday are looking mostly dry, however, a decent
subset of ensemble members (~40%) do show a weakening front
approaching the the Pacific Northwest from an upper level system
progressing over the northeast Pacific into British Columbia.
The front looks like it mostly dies off before reaching our
area, however there is a slight chance (15-20%) that we could
see some lingering showers along the coast and southwest
Washington.      -Alviz/Schuldt
&&
.AVIATION...Predominately MVFR ceilings persist across NW Oregon
and SW Washington due to a strong marine layer. High pressure over
the area is helping thin out the marine layer today with satellite
imagery showing cloud cover is starting to dissipate. Expecting
clouds to scatter out amount 20-21z inland and around 23z for the
coast though, clouds around KAST may stick around for a bit
longer. Another repeat is expected tonight with stratus moving in
along the coast between 04-06z Sat and between 10-12z Sat inland.
Probabilities for sub-VFR CIGs along the coast are >80% while
inland they are between 40-60%. Winds remain northerly through the
day at 10 kts or less.
KPDX AND APPROACHES...MVFR CIGs hold on until 20-21z then scatter
out this afternoon. Winds from the north around 5 kt. Another
round of stratus is expected to move in between 10-12z Sat,
bringing MVFR CIGs. -Batz
&&
.MARINE...High pressure over the waters today with winds mainly
from the north, though becoming variable for a brief period
late this morning. Winds remain less than 10 kts with gusts
below 15 kts, with seas 5-6 ft at 12-14 seconds.
A surface front moves through the waters late Saturday into early
Sunday. Winds shift southerly ahead of the frontal passage
Saturday, then increase as the front passes to 15-20 kts with
gusts up to 20 kts, locally up to 21-22 kts in the far outer
waters. Probabilities for wind gusts of 21 kt or greater (small
craft advisory criteria) are 50-70% when looking at 24 hour
periods for Saturday and Sunday. However, when looking closer at
the hourly probabilities, chances drop significantly to 10-30% at
the highest on either day, with highest probabilities for the far
outer waters around 40-60 nm from the coast. This indicates that
small craft gusts are possible but likely won`t be widespread or
long duration. This combined with the smaller area of potential
small craft advisory winds leads to low chances of a small craft
advisory being issued, though will still continue to monitor the
forecast as it changes. Seas remain around 5-8 feet at 10-12
seconds through Sunday. The forecast for the northwest swell has
decreased, leading to less than 25% chance of seas reaching 9 feet
and less than 10% chance of seas reaching 10 feet Sunday.  -HEC
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&
$$
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NWS PQR Office Area Forecast Discussion