327
FXUS66 KPQR 031636 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
936 AM PDT Wed Sep 3 2025

Updated Aviation Discussion

.SYNOPSIS...Inland high pressure will bring continued hot
weather to much of the region through the workweek, with
widespread Moderate HeatRisk inland and pockets of Major
HeatRisk in the Columbia Gorge and Hood River Valley. A compact
disturbance moving north from California will trigger scattered
showers and isolated thunderstorms again this afternoon and
evening, mainly near the Cascades and foothills. A pattern shift
will favor cooler and wetter conditions by the weekend.

&&

.SHORT TERM...Now through Friday Night...Upper-level ridging
extending from the Great Basin over the Interior Northwest will
peak in amplitude today before beginning to erode through the
remainder of the workweek. Meanwhile, as a broad upper low over
the northeastern Pacific continues to retrograde away from the
coast, a compact shortwave near Cape Mendocino early this
morning will track northward along the western Oregon coast
through tonight, then off the western Washington coast on
Thursday. This feature will support afternoon and evening
showers and isolated thunderstorms along the Cascades and
foothills as it transits overhead. Southeasterly flow aloft will
see any storms and/or outflow clouds from convection move to
the west across the Willamette Valley and toward the Coast
Range. These outflow clouds will help depress temperatures
slightly today due to decreased insolation, as will any showers
that manage to reach the ground. Some additional showers and
storms may develop on Thursday as the wave lifts northward, but
both occurrence and coverage of storms remains low confidence.

In the Columbia Gorge and Hood River Valley, temperatures will
be very similar today and Thursday as the majority of convection
is expected to remain to the south and west. The combination of
afternoon highs in the low to mid 90s and overnight lows in the
mid 60s to low 70s tonight will yield continued Major HeatRisk,
and the Heat Advisory has therefore been extended through 8 PM
Thursday. Conditions will begin to trend cooler Thursday night.

Across other inland valleys, expected high cloud cover will see
high temperatures remain largely in the upper 80s to around 90
degrees today, with slightly cooler temperatures in the Coast
Range and Cascades and much cooler along the coast. Overnight
lows will range from the mid 50s in coastal areas to mid 60s in
the Portland/Vancouver Metro. As the shortwave lifts northward
on Thursday, temperatures may actually end up a few degrees
warmer in many areas as cloud cover decreases, before the
weakening ridge sees temperatures trend cooler beginning on
Friday. Widespread Moderate HeatRisk will therefore continue
across inland areas through Thursday for most, and into Friday
in the northern Willamette Valley and Portland/Vancouver Metro
where overnight lows remain the highest. -Picard


.LONG TERM...Saturday through Tuesday...Upper-level troughing
initially developing over the northeastern Pacific this weekend
looks to move inland early next week, bringing much cooler and
potentially wetter weather to the region. There is moderate to
high chances, roughly 50-75%, that high temperatures will remain
in the 70s across inland valleys on Saturday, increasing to
65-90% by next Monday as temperatures are favored to remain
below normal. In general, about half of long-range ensemble
members also show accumulating precipitation across the region
early next week as chances for rain increase ahead of the
approaching upper trough. -Picard

&&

.AVIATION...Expect VFR conditions to persist through the TAF
period at inland sites. High based convective debris will continue
to stream overhead from southern Oregon through the afternoon
which is resulting in lowered flight conditions persisting along
the coast. Clearing upper level clouds and daytime heating should
help improve conditions towards MVFR around 20Z-22Z Wednesday for
coastal locations. However, flight conditions are expected to
lower again towards IFR/LIFR around 00Z-02Z. Could see some
northerly gusts along the coast this afternoon up to 20 kt.

It`s worth mentioning Wednesday will also bring another chance
for scattered showers and thunderstorms, possibly a bit more
abundant as a more robust system moves over the region. That said,
the bulk of the activity likely remains near the Cascades in and
around central Oregon. The terminals to watch during the 21Z-06Z
Thursday time period when activity is most abundant will be KSLE
and KEUG, but confidence in placement/timing is not nearly high
enough to add a mention of thunderstorms/showers to those TAFs as
of the 12Z package.

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 from time to time. Winds generally remain
below 10 knots. /42-Schuldt

&&

.MARINE...A ridge of high pressure continues to build over the
far eastern Pacific today with little in the way of marine
concerns through the end of the week and beyond. Expect the
aforementioned ridge of high pressure to help tighten surface
pressure gradients along the coastline leading to an increase in
northerly winds compared to past days. Confidence is high
(75-85%) peak gusts in the afternoon/evening hours generally
remain in the 15-20 knot range, just below Small Craft Advisory
Criteria, with the probabilities for 21 knot gusts of above only
around 15-30% today and Thursday - probabilities fall off to
0-5% after this point. Seas hold around 4-6 ft through the first
half of Friday due to an increase in wind waves and a fresh
northwesterly swell. After this point, seas back-off into the
2-4 ft range over the weekend into early next week. -Schuldt

&&

.FIRE WEATHER...A compact disturbance will lift northward from
near Cape Mendocino early this morning along the Oregon Coast
through tonight and into western Washington by Thursday. Ahead
of the passing system, support for convection will coincide with
elevated instability to generate 15-25% chances for scattered
rain showers and isolated thunderstorms through the afternoon
and evening today and possibly into Thursday.

Dry low-level flow will see minimum relative humidities of
25-35% today along the Cascades, and 30-50% in the foothills,
with high cloud bases also favoring sub-cloud evaporation of any
rainfall (virga). This set-up will allow for dry thunderstorms
to initially develop over areas of terrain before tracking away
to the northwest toward valley areas. Even in slower-moving
storms which may bring localized rain, lightning strikes can
extend well away from any narrow rain cores. Additionally, the
evaporation of rain beneath the cloud may also generate gusty
and erratic downdraft winds, in some cases many miles away from
the parent storm.

Given the potential for dry lightning and gusty winds, as well
as receptive fuels, there remains elevated potential for new
fire starts across the Willamette, Mt. Hood, and Gifford Pinchot
National Forests today. Red Flag Warning therefore remain in
effect across these areas (Fire Weather Zones 634/635 in SW
Washington, and FWZ 688/689/690 in NW Oregon) through 9 PM this
evening. Additionally, high instability may also enhance
pyroconvective activity over ongoing fires in these areas even
in the absence of thunderstorms.

The disturbance will weaken as it tracks northward on Thursday,
lowering confidence in the occurrence of additional convection.
Existing Red Flag Warnings may be extended if chances increase
for additional dry thunderstorm. -Picard

&&

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

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

     Red Flag Warning until 9 PM PDT this evening for ORZ689-690.

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

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

PZ...None.

&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
x.com/NWSPortland