417
FXUS66 KPQR 301020
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
320 AM PDT Sat Aug 30 2025

.SYNOPSIS...A cutoff low lingering offshore of northwestern
Oregon and southwestern Washington will bring continued
seasonable temperatures through Labor Day Weekend with morning
incursions of marine clouds giving way to breaks of afternoon
sun. Building high pressure will yield a significant warming
trend early in the week, with increasing confidence in high
temperatures reaching the 90s and Moderate to Major HeatRisk
Tuesday through at least Thursday across inland areas.

&&

.SHORT TERM...Now through Monday Night...Latest water vapor
satellite imagery features a broad cutoff low offshore of the
central Oregon coast. This low will continue to meander close to
the coast through Sunday before retrograding away to the west as
it pivots about the northern flank of another cutoff low well
offshore of northern California. Relatively cool but seasonable
mid-level air of 15-18C at 850-hPa overhead will keep surface
temperatures near to slightly above normal inland and near to
slightly below normal along the coast, yielding very pleasant
conditions for travelers through the holiday weekend. Onshore
flow will allow for overnight incursions of marine stratus up
the Columbia River and through Coast Range gaps into interior
lowlands, before breaking out to increased sun by late morning
or early afternoon as diurnal mixing strengthens. -Picard


.LONG TERM...Tuesday through Friday...As the aforementioned
cutoff low exits westward and opens into upper-level troughing
over the Gulf of Alaska by the latter half of the week, narrow
but high-amplitude upper ridging is favored to build northward,
extending from the Great Basin across the Pacific Northwest and
into interior British Columbia through the midweek period. There
remains one major source of uncertainty however: the remnant
upper low associated with a tropical disturbance currently off
the coast of Mexico which may track to the north and inland
over northern California.

This approaching low could affect the forecast in a few ways.
If it remains weaker and to the south or dissipates before
moving into western Oregon, temperatures would be favored to
remain on the warmer side of ensemble guidance, producing around
a 25% chance that temperatures along the I-5 corridor reach 100
degrees on Tuesday and Wednesday afternoons. Conversely, if the
low remains deeper as it moves into southwestern Oregon, the
anomalous southeasterly flow could aid in developing convection
along the Cascades as well as pushing high clouds downstream
toward the coast. This scenario would yield lower insolation
and therefore cooler temperatures, supporting a 25-35% chance
that high temperatures remain below 90 degrees Wednesday and
Thursday afternoons. Forecast confidence therefore remains
only moderate, with particularly low confidence in regard to
the occurrence or location of any convection.

Overall, a significant warming trend is expected, with 45-65%
chances high temperatures surpass 95 degrees across inland
valleys on Wednesday and Thursday. Low temperatures are also
favored to remain above average through the period, with
generally 35-65% chances of temperatures remaining above 65
degrees Wednesday and Thursday nights in the Willamette Valley
north of Albany/Corvallis through the Portland/Vancouver metro,
as well as in the Cascade foothills and Columbia Gorge. In the
southern Willamette Valley and the Lower Columbia and Cowlitz
Valleys, chances to remain above 65 degrees overnight are lower,
15-35%. Especially compared to the background climatology of
declining temperatures, these warm to hot conditions could again
result in widespread Moderate to locally Major HeatRisk. -Picard

&&

.AVIATION...Marine stratus continues to support largely MVFR
cigs at coastal terminals as of 10z Sat, as well as inland along
the Lower Columbia as far as KKLS. MVFR cigs are favored to
continue, with increasing chances of IFR cigs along the central
OR coast, up to 60-70% at KONP, through 17-18z Sat before mixing
increases and favors a break out to largely VFR cigs. An area of
low pressure meandering offshore may bring light rain showers to
coastal terminals, most likely at KAST where there is a 15-25%
chance, with lesser chances to the south. Inland, continued VFR
conditions remain the most likely outcome, however there is a
30-40% chance of MVFR cigs as stratus develops through the
remainder of the overnight period, with any restricted cigs
expected to improve rapidly from 17-19z Sat. Light and variable
winds this morning will build to 5-10 kt out of the north to
northwest, before easing to less than 5 kt by 06z Sun.

PDX AND APPROACHES...VFR cigs favored with a 30-40% chance of
MVFR cigs through 17-18z Sat. Otherwise, VFR conditions expected
with northwest winds around 5 kt. -Picard

&&

.MARINE...Benign conditions will continue across the coastal
waters through the Labor Day Weekend with light southerly winds
early this morning backing out of the north to northwest by
this afternoon and seas continuing at 2-4 ft. As high pressure
strengthens, northerly winds will increase through midweek,
with high chances, greater than 70%, of maximum wind gusts
exceeding 20 kt across the outer waters Tuesday and Wednesday
afternoons, conditions which may be hazardous to small craft.
A building northwesterly swell will see seas rise to 5-6 ft late
Tuesday into Wednesday. -Picard

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

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