South Beach, Oregon Weather Forecast Discussion

367
FXUS66 KPQR 222223
AFDPQR
Area Forecast Discussion
National Weather Service Portland OR
323 PM PDT Mon Sep 22 2025
.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
conditions with largely clear skies and unrestricted vis. Diurnal
winds of 5-10 kt out of the north to northwest inland and 10-15 kt
with gusts around 20 kt along the coast this afternoon will ease
to 5 kt or less this evening into tonight. East winds at the
surface are favored along and west of the Columbia River Gorge at
KTTD and at the coast beginning after midnight tonight, with more
widespread easterly flow above the nocturnal inversion at 1-2 kft.
Periods of marginal low-level wind shear are possible overnight
into Tuesday morning, before east-northeasterly flow mixes down to
the surface at Portland-area terminals after 18z Tue.
KPDX AND APPROACHES...VFR conditions favored throughout the
period beneath building high pressure. Northwest flow at 5-10 kt
will ease below 5 kt this evening into tonight. Easterly flow
at the surface will develop west of the Columbia River Gorge near
KTTD after midnight, but KPDX/KVUO will be more likely to see
light northerly to north-northeasterly winds. With gusty easterly
flow above 1-2 kft, periods of marginal low-level wind shear are
possible overnight into Tuesday morning, before east-northeasterly
winds mix down to the surface after 18z Tue.       -Picard
&&
.MARINE...Building surface high pressure over the northeastern
Pacific will continue to support northerly winds of 10-15 kt
across the waters. Regional buoys are reporting seas of 8-12 ft
at 10-12 seconds, or at marginal Small Craft Advisory levels;
current hazards will therefore remain in effect through 11 PM PDT
this evening as seas slowly subside below hazardous criteria. The
respite may be brief, however, as thermal troughing along the
coast will yield a tightening pressure gradient and high
confidence in wind gusts reaching 20-25 kt late Tuesday through
Wednesday. Seas of 7-9 ft at 10-12 seconds tonight into Tuesday
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
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ251>253-
     271>273.
&&
$$
www.weather.gov/portland
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NWS PQR Office Area Forecast Discussion