824
FXUS66 KPQR 032156
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
256 PM PDT Wed Sep 3 2025

.SYNOPSIS...High pressure inland continues to drive hot weather
across much of the region, with widespread Moderate HeatRisk and
localized Major HeatRisk focused in the Columbia Gorge and Hood
River Valley. A compact disturbance that moved north from
California into western Oregon today will bring scattered
showers and isolated thunderstorms mainly along the Cascades and
foothills this afternoon and evening. A shift in the pattern
later this week will allow cooler and wetter weather to arrive
by the weekend.

&&

.SHORT TERM...Now through Friday Night...The ridge over the
Interior Northwest has started to weaken as a compact shortwave
that moved out of northern California earlier today lifts
through western Oregon. This disturbance is providing lift and
instability, which will allow showers and isolated
thunderstorms to develop along the Cascades this afternoon and
evening. Southeasterly flow may carry some cloud debris and
outflow into the Willamette Valley and Coast Range, which may
help limit heating in some locations.

Temperatures across the inland valleys will top out in the
upper 80s to near 90 today, with the Gorge and Hood River Valley
expected to climb into the low to mid 90s. Overnight lows will
again stay warm - mid 60s to low 70s in the Gorge and
Portland/Vancouver Metro, 50s to 60s elsewhere. This continues
to support Major HeatRisk in the Gorge and Hood River Valley
where a Heat Advisory remains in effect through 8 PM Thursday.

This weakening compact low will lift north into western
Washington by Thursday, keeping some chances for additional
convection mainly near the Cascades, though coverage looks less
widespread. With cloud cover thinning tomorrow, highs may end up
a few degrees warmer than today across the Willamette Valley
and other inland areas. By Friday, cooler temperatures become
more noticeable as the ridge weakens further, with highs
trending down a few to several degrees and HeatRisk lowering to
mostly Minor inland, except for locally higher values in the
northern Willamette Valley and Gorge where overnight lows remain
elevated.

.LONG TERM...Saturday through Tuesday...A more significant
change sets in this weekend as troughing strengthens over the
northeast Pacific and begins to shift inland. This will bring a
cooling trend with moderate to high probabilities (50-75%) that
inland valleys dip below 80 degrees on Saturday, with even
higher probabilities (70-90%) by Monday. Precipitation chances
also increase with this shift, though ensemble guidance varies
on amounts. Roughly half of solutions suggest measurable rain
sometime early next week, especially near the Cascades and along
the coast. Overall, expect a turn toward cooler, unsettled
weather beginning this weekend and continuing into early next
week. ~Hall


&&

.AVIATION...Expect VFR conditions to persist through the TAF
period at inland sites. High based convective debris along with a
broad area of high pressure over the waters that will help
maintain the current IFR/LIFR conditions along the coast.

Scattered showers and thunderstorms remain in the forecast as a
more robust system moves over the region. That said, the bulk of
the activity is expected to remain near the Cascades in and
around central Oregon. Through 06Z Thursday, KEUG and KSLE will
have the highest probability for showers and thunderstorms
(15-20% probability), but confidence in placement/timing is not
nearly high enough to add a mention of thunderstorms/showers to
the TAFs at this time.

Also, if traveling over the Cascades, be aware of smoke/haze from
wildfires over the region.

PDX AND APPROACHES...VFR conditions persist with high cloud cover
streaming overhead. Winds generally remain below 10 knots.
/42-Schuldt

&&

.MARINE...Minimal change in the overall forecast today. A ridge
of high pressure continues to build over the far eastern Pacific.
This ridge will bring stronger northerly winds across all waters
with gusts up to 20 kt during the afternoons and evenings through
the end of the week. As the weekend approaches, a pattern change
is expected as a broad area of low pressure from the Gulf of
Alaska will slowly start to move southward. This will result in
winds weakening and then becoming more southerly by Saturday with
winds remaining below Small Craft Conditions.

Seas hold around 4-6 ft through Friday due to an increase in wind
waves and a fresh northwesterly swell. Afterwards, seas subside
towards 2-4 ft by the weekend and into early next week.

Broad high pressure over the waters will also bring about the
probability of dense fog, primarily for the inner waters and the
Columbia River Bar. Therefore, have issued a Dense Fog Advisory
starting at 8PM tonight through 11AM Thursday morning as
visibilities are expected to fall below 1 NM. It should be noted,
that there remains some uncertainty in the exact timing of the
dense fog. /42

&&

.FIRE WEATHER...
A compact low that lifted north into western Oregon today has
triggered scattered showers and isolated thunderstorms across
the Cascades this afternoon, with activity expected to persist
into the evening. Southeasterly flow aloft has been steering
some storm outflows and cloud debris westward toward the valleys
and Coast Range. Dry low-level conditions remain in place, with
minimum RH values of 25-35% along the Cascades and 35-50% in
the foothills. High storm bases and dry air in the atmosphere
continues to keep thunderstorms dry and outflows gusty and
erratic. Even slow moving cells producing localized rainfall
remain capable of ignitions, as lightning strikes can occur well
away from rain cores.

With todays instability and dry fuels, there remains elevated
potential for new fire starts across the Willamette, Mt. Hood,
and Gifford Pinchot National Forests. Red Flag Warnings remain
in effect through 9 PM this evening for Fire Weather Zones
634/635 in southwest Washington and 688/689/690 in northwest
Oregon. In addition to new ignitions, ongoing fires may
experience enhanced pyroconvective activity under the unstable
environment. As the disturbance weakens and lifts into
Washington on Thursday, the coverage and confidence of
additional thunderstorms decrease. Red Flag highlights for
Thursday will depend on whether instability remains sufficient
to support new convection.
~Hall/Picard

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 9 PM PDT this evening for ORZ688>690.

     Heat Advisory until 8 PM PDT Thursday for ORZ120>122.

WA...Red Flag Warning until 9 PM PDT this evening for WAZ634-635.

     Heat Advisory until 8 PM PDT Thursday for WAZ209-210.

PZ...Dense Fog Advisory from 8 PM this evening to 11 AM PDT
     Thursday for PZZ210-251>253.
&&

$$

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