288
FXUS66 KPQR 022203
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
303 PM PDT Tue Sep 2 2025

.SYNOPSIS...
High pressure strengthening inland through midweek will bring
hot weather to much of the region, with valley highs near 90
degrees and warm overnight lows in the 60s. HeatRisk will be
Moderate in most areas, with pockets of Major HeatRisk in the
Gorge and Hood River Valley. An upper low moving north from
California will trigger scattered showers and isolated
thunderstorms this evening and again Wednesday, mainly near the
Cascades. By the weekend, a shift in the weather pattern will
favor cooler temperatures and an increasing chance for showers.

&&

.SHORT TERM...Now through Thursday Night...The upper low that
kept conditions cooler over the Holiday weekend is drifting west
into the Pacific, while upper ridging expands northward from
the Great Basin. Meanwhile, a compact disturbance offshore of
California is forecast to move inland tonight and into Oregon
early Wednesday, providing the lift necessary for showers and
isolated dry thunderstorms along the Cascades through midweek.

Inland valleys will rise into the upper 80s to low 90s today,
with the Columbia Gorge and Hood River Valley reaching the mid
to upper 90s. The coast remains cooler in the 60s to 70s. Warm
nights will provide little relief, with lows generally in the
mid to upper 60s in the Willamette Valley and Cascade foothills,
near 70 in the Gorge, and 50s to low 60s elsewhere. This
combination of hot afternoons and warm nights will generate
widespread Moderate HeatRisk, with localized Major HeatRisk in
the Gorge and Hood River Valley. A Heat Advisory remains in
effect for these areas through Wednesday evening.

Dry thunderstorm chances will focus on the Cascades - starting
mainly in Lane and Linn County Cascades, then expanding
northwest into north Oregon Cascades this evening into early
Wednesday morning. Additionally, southeasterly flow aloft may
push thunderstorms to the west overnight, affecting the southern
Willamette Valley and inner coastal waters near Newport, OR.
Wednesday morning into the afternoon, thunderstorms will be
mostly confined to the northwest Oregon Cascades. Given the dry
subcloud layer, lightning without much rainfall is possible,
raising concerns for dry strikes.

By Thursday, the low begins to weaken and lift north, leading to
fewer storms and slightly cooler temperatures. Cloud debris or
showers may also limit daytime heating in places. Note,
thunderstorms may still remain possible on Thursday, but
confidence remains low at this time.

.LONG TERM...Friday through Monday...By late week, forecast
ensembles show a shift toward troughing over the northeast
Pacific, ending the hot pattern and steering temperatures back
toward seasonal levels. Cooling is expected to continue into
early next week, with some areas trending below normal. The
broad offshore trough should also bring increasing moisture and
improve chances for showers, particularly along the coast and
Cascades. While details remain uncertain, the overall signal
points toward a cooler and potentially wetter stretch developing
from the weekend into next week.
~Hall

&&

.AVIATION...VFR conditions expected for the next 24 hours at
inland sites. Along the coast, VFR conditions until marine stratus
forms once again overnight. Expect MVFR/IFR ceilings to form at
KONP by 00-04z Wed, slowly spreading north along the coast to form
at KAST by 07-11z Wed. Ceilings should return to VFR conditions by
16-20z Wed with daytime heating. Mainly northwest winds along the
coast, increasing to around 10 kts after 19z Tue, with gusts up to
20 kts around KONP through around 00-03z Wed. Inland winds
generally light from the north to northwest.

A weather system will begin producing shower and thunderstorm
chances over the central Oregon Cascades after 00z Wed. Some
showers and possibly a thunderstorm could be possible into the
Willamette Valley after 10z Wed. Current thunderstorm probability
is less than 10% chance at any valley terminal, so no mention in
the TAFS, but have included VCSH in KEUG TAF. These chances could
spread north to KSLE by 16-19z Wed, but probability is too low to
add to TAF at this time. Winds will also shift west to southwest
in the southern Willamette Valley at this time.


PDX AND APPROACHES...VFR conditions next 24 hours. Winds stay
fairly light out of the northwest. -HEC

&&

.MARINE...Fairly benign late-summer like conditions are expected
through the rest of the week into the weekend. A weak surface low
pressure off southwest Vancouver Island gradually moves westward
the next several days with high pressure strengthening across the
coast waters. This progression will tighten surface pressure
gradients, allowing for increasing northerly winds during the
afternoon and evening hours, especially on Wednesday and Thursday.
Peak wind gusts during the mid-week period likely sit in the
15-20 knots range with probabilities for small craft conditions of
gusts over 21 kts only around 10-20%. Seas increase to around 4-6
ft this afternoon due to an increase in wind waves and a fresh
northwesterly swell. Expect seas to hold in this 4-6 ft range
through Friday before backing off slightly over the weekend into
next week. -Schuldt/HEC

&&

.FIRE WEATHER...A low pressure system lifting north from
California into Oregon on Wednesday and Washington by Thursday
will bring a heightened risk for dry thunderstorms.
Southeasterly flow aloft will increase lift and instability
while surface conditions remain dry, with relative humidity
bottoming out near 20-30% along the Cascades and 30-40% in the
foothills. This setup will favor thunderstorm development over
the Oregon Cascades this evening, with activity drifting into
foothills and valley locations overnight.

High cloud bases will allow much of the rainfall to evaporate
before reaching the ground, making dry lightning and gusty,
erratic outflow winds possible. While slower-moving storms could
bring localized rain, lightning strikes may extend well away
from rain cores. Given the very receptive fuels, new fire starts
are possible, especially in the Willamette NF where a Red Flag
Warning continues for Zones 689 and 690. Strong instability may
also enhance pyroconvective activity for ongoing fire.

By Wednesday, the low weakens as it tracks farther north,
lowering confidence in widespread dry lightning. However,
elevated instability will persist in southeastern Lane County,
supporting the extensions of the Red Flag Warning through 9 PM
Wednesday. To the north, a Red Flag Warning has been issued for
Zones 634, 635, and 688 - including the Mt. Hood and Gifford
Pinchot NFs from 12 PM to 9 PM Wednesday.
~Hall

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from noon to 9 PM PDT Wednesday for ORZ688.
     Heat Advisory until 9 PM PDT Wednesday for ORZ120>122.
     Red Flag Warning until 9 PM PDT Wednesday for ORZ689-690.
WA...Red Flag Warning from noon to 9 PM PDT Wednesday for WAZ634-
     635.
     Heat Advisory until 9 PM PDT Wednesday for WAZ209-210.
PZ...None.
&&

$$

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