Siouxon Trail, Washington Weather Forecast Discussion

373
FXUS66 KPQR 040918
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
218 AM PDT Sat Oct 4 2025
.SYNOPSIS...Scattered showers with cooler conditions continue
through Saturday evening. Warmer temperatures and offshore
flow develops Sunday and continues through Tuesday, bringing an
extended period of dry weather with breezy east to northeast
winds and daytime high temperatures in the 70s across the
lowlands.
&&
.DISCUSSION...Saturday through Friday...A weak shortwave trough
is slated to move from north to south over NW Oregon and SW
Washington today, and IR satellite imagery early this morning
depicts high clouds moving across the region ahead of this
shortwave. Scattered showers are expected across the region
associated with this shortwave through this evening. Widespread
rain is not expected. There will be limited accumulation with
these showers, though some stronger showers could produce brief
moderate rainfall.
Ensemble guidance is in good agreement that upper level ridging
will quickly build west from the eastern Pacific over the PacNW
Sunday into Monday, and a surface thermal trough will form along
the Oregon and southern Washington coast. This pattern will
result in the return of dry weather with warming temperatures.
After one more day of temperatures in the 60s today, expect
temperatures to rise back into the 70s. Additionally, ensemble
guidance continues to suggest surface pressure gradients will
tighten over the Cascades and Willamette Valley, resulting in
elevated offshore winds Sunday through Monday night. North winds
will increase in the Willamette Valley in the late morning
through evening hours with gusts up to 20-25 mph possible,
mainly south of McMinnville. Easterly winds begin increasing
over the Cascade crest in the afternoon hours, then spread into
the valleys and foothills in the evening and overnight hours,
with gusts up to 20-25 mph, locally up to 30 mph in wind prone
gaps and valleys. East winds will be strongest through the
Columbia River Gorge, especially on Monday night, with gusts up
to 30-40 mph. Although atmospheric conditions will be drying
out, causing daytime relative humidity values to fall quite
significantly, the recent rains will limit any fire weather
concerns. Still, those burning should use caution on Sunday and
Monday.
On Tuesday, the high pressure and thermal trough will begin
breaking down later in the day due to an upper level low
pressure system approaching the region, allowing winds to begin
shifting onshore again, though dry and warm conditions are
expected to continue. However, Wednesday and beyond, the
forecast becomes very uncertain as ensembles are split on how to
resolve the aforementioned upper level low. About half of the
ensemble members suggest the low will deepen right along the
Washington and Oregon Coast, and the other half suggest the low
will deepen just west of the coast Wednesday through Friday. The
first scenario would bring the return of cooler temperatures and
shower chances to NW Oregon and SW Washington, whereas the later
scenario would keep conditions dry and on the warmer side. The
NBM 25th percentile to 75th percentile temperature spread for
Wednesday and Thursday ranges from the low 60s to mid 70s. The
deterministic NBM (which our forecast reflects) introduces
15-35% chance of rain Wednesday through Friday, increasing to
around 45-60% chance Friday evening. -03
&&
.AVIATION...A weak shortwave trough will brush the region
through Saturday, bringing scattered showers through 03-06z
Sun. Lowered flight levels expected along the coast, lifting
around 19-21z Sat. North of KTMK, expect mainly MVFR ceilings
with a 40-60% chance of IFR ceilings after 12z Sat. South of
KTMK has a 70-90% chance of IFR ceilings. With onshore flow
present through the TAF period, stratus development along the
Cascade foothills is possible, which could build westward into
the Valley. This produces a 40-70% chance for MVFR CIGs between
11-18Z Sat for the Willamette Valley, with highest chances
south of KUAO. Otherwise, winds will remain light and variable
through the TAF period.
KPDX AND APPROACHES...Expect mostly VFR conditions through the TAF
period. CIGs could lower between 11-18Z Sat, with a 30-50%
chance of MVFR CIGs. Light and variable winds through the
period. -03
&&
.MARINE...Surface high pressure builds over the waters today with
winds shifting northwesterly, remaining under 15 kt today.
On Sunday, stronger high pressure and tightening pressure
gradients due to a thermal trough developing along the coast will
shift winds northeasterly and allow winds to increase. Guidance
suggests high confidence (60-80% chance) that the waters beyond 10
NM south of Cape Falcon will experience northeasterly wind gusts
up to 25 kt (small craft conditions) on Sunday late morning
through the evening hours. Elsewhere, these chances remain around
20% or less. Winds remain northeasterly Monday, but gusts will
mainly be less than 20 kts. Seas fall to 4-6 ft on Saturday and
hold through early next week. -03
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT early this morning for
     PZZ272-273.
&&
$$
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NWS PQR Office Area Forecast Discussion