Orenco, Oregon Weather Forecast Discussion

697
FXUS66 KPQR 230346 AAC
AFDPQR
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
841 PM PDT Mon Sep 22 2025
Updated multiple discussions
.SYNOPSIS...High pressure will bring warm and dry conditions
through mid-week. A thermal trough developing tonight and
Tuesday night will bring increased offshore flow each night,
especially over the Cascades and Columbia River Gorge. Cooler
temperatures return Thursday with increased onshore flow.
&&
.SHORT TERM...Now through Wednesday night...Warm, dry, and
sunny conditions prevail across northwest Oregon and southwest
Washington today as an upper level ridge sets up over the
Pacific Northwest. Upper level troughs over the Gulf of Alaska,
Southern California, and the Rockies is amplifying the ridge
over our area and bringing the warm and dry air. Still expect
seasonable high temperatures this afternoon, with mid 70s across
interior valleys and 60s along the coast.
Tonight, a thermal trough will set up along the coast with
higher surface pressure inland, returning light easterly winds.
Based on the set-up of the thermal trough, we should see these
easterly winds downsloping off the Cascades and Coast Range.
Wind speeds are dependent on pressure gradients, and right now
models are honing in on a -3 to -5 mb forecast gradient across
the Cascades and Columbia River Gorge. This would result in
easterly gap winds through the Columbia River Gorge with gusts
to 25-35 mph, strongest over surrounding ridgetops such as Three
Corner Rock or Crown Point.
Across the high Cascades and Cascade Valleys, the strongest
easterly winds will be along crest (50-70% chance for gusts of
25 mph or greater), but most locations generally remain under 25
mph. NBM/HREF suggests only a 5-15% chance for wind gusts of 25
mph or greater across the Cascades below crest level. Meanwhile,
pressure gradients are weaker along the Coast Range, so
downsloping easterly winds should be very light (around 10 mph
or less). These easterly winds will result in poor to moderate
overnight humidity recoveries across the Cascades, lowest over
the Linn and Lane County Cascades where maximum relative
humidities (RHs) will struggle to rise above 30-35% tonight.
Despite near-critical RHs tonight for the Linn and Lane County
Cascades, wind gusts above 25 mph will not be widespread enough
outside of the crest to warrant any issuance of fire weather
headlines. On the converse, while the Gorge may be reaching RFW
criteria, recent wetting rains and RHs forecast above critical
thresholds will also prevent any issuance of fire weather
headlines. Though no RFWs have been issued for tonight`s
offshore flow, fire weather concerns remain elevated and will
need to be closely monitored.
Pressure gradients ease on Tuesday, so winds will also gradually
weaken throughout the day with gusts falling below 15 mph by the
afternoon. Tuesday to Wednesday will be the warmest and driest
days of the week as the upper level ridge continues to amplify,
leading to above-normal temperatures and relative humidities
around 30% or lower for most places west of the Coast Range.
Afternoon highs each day are forecast in the mid 80s across
interior valleys, and upper 60s to low 70s along the coast. The
thermal trough does re-develop Tuesday night into early
Wednesday morning, but pressure gradients don`t appear to be as
tight as they will be tonight, therefore, don`t expect any
stronger offshore flow. Light onshore flow returns by Wednesday
afternoon as the thermal trough completely breaks down.
                                                    -Alviz
.LONG TERM...Thursday through Sunday...On Thursday, most ensemble
members are in agreement that the ridge begins to flatten as another
trough dips southward into British Columbia from the Gulf of Alaska.
While we still remain dry, cooler temperatures return as onshore
flow strengthens from a tightening pressure gradient. Friday, there
remains uncertainty with the weather pattern. About half of the LREF
ensemble members show the trough dipping far enough south to bring
cooler temperatures and light precipitation along the north
Oregon/south Washington coasts. The other half of ensemble members
maintain zonal flow or slight ridging, which would keep us warmer
and drier.
By the weekend, there remains even more uncertainty in the
pattern but most ensemble members generally keep us dry on
Saturday. About half of the members are beginning to show a
stronger system in the northeast Pacific, but there remains high
uncertainty on the exact track, magnitude and timing of the
system if it were to enter our area. Only about 15% of members
show this system bringing a widespread soaking rain across
northwest Oregon and southwest Washington by Sunday.   -Alviz
&&
.AVIATION...Building high pressure will see widespread VFR under
clear skies and unrestricted vis, with northwest flow below 5 kt.
There could be some lowered flight conditions along the coast,
primarily around KOPM through 17Z Tue. East winds at the surface are
favored along and west of the Columbia River Gorge at KTTD and at
the coast beginning around 10Z-12Z Tuesday, with more widespread
easterly flow above the nocturnal inversion at 1-2 kft.
Low-level wind shear possible through 00Z Wed for KPDX and
KVUO. It should also be noted that low-level wind shear in
the form of speed shear could also be experienced near KTTD
through the same time period. East-northeasterly flow mixes
down to the surface around 00Z Wed.
KPDX AND APPROACHES...VFR conditions with northwest flow below 5
kt. Gusty easterly flow above 1-2 kft will result in periods of
low-level wind shear from around 10Z Tuesday to around 00Z
Wednesday. Expect east-northeasterly winds mix down to the
surface around 00Z Wednesday with gusts up to 20 kt. After 03Z
expect winds less than 10 kt. /42-Picard
&&
.MARINE...Building surface high pressure over the northeastern
Pacific will continue to support northerly winds of 10-15 kt
across the waters. Buoys continue to report seas of 7-11 ft at
10-12 seconds. This is resulting in Small Craft Advisory
conditions, therefore will maintain the current hazards through
Tuesday morning. There could be brief periods of sub Small Craft
conditions, however, as thermal troughing along the coast will
yield a tightening pressure gradient and high confidence in wind
gusts up to 25 kt late Tuesday through Wednesday. Seas of 7-9 ft
at 10-12 seconds Tuesday afternoon will build again to 8-10 ft
midweek as winds increase, with additional Small Craft Advisories
very likely across the waters midweek. Conditions then improve as
winds and seas ease into the weekend as high pressure weakens.
-Picard/42
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 AM PDT Tuesday for PZZ210-
     251>253-271>273.
&&
$$
www.weather.gov/portland
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NWS PQR Office Area Forecast Discussion