653
FXUS66 KPQR 210510
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1010 PM PDT Thu Aug 20 2026

Updated aviation discussion.

&&

.SYNOPSIS...Low pressure brings chances for showers Friday
evening into Saturday across northwest Oregon and southwest
Washington, with a 15-20% chance for thunderstorms over the
Cascades and 5-10% chance elsewhere. Winds out of the
north/northwest, will shifts towards the west/southwest on
Saturday. Seasonable weather returns Sunday through the middle
of next week.

&&

.DISCUSSION...Tonight through Wednesday...Tonight into Friday
morning, low temperatures around 60-65 degrees across the
Portland/Vancouver Metro, Columbia River Gorge, and Cascade
foothills will result in limited overnight relief from the heat.
Chances for low temperatures remaining above 65 degrees are
around 15-25% for the Portland/Vancouver Metro and 60-80% along
the Columbia Gorge.

The potential for limited overnight relief in addition to the
afternoon heat will result in Moderate HeatRisk today along
portions of the I-5 corridor and Columbia Gorge. This means that
this level of heat will affect those sensitive to heat, especially
those without adequate cooling or hydration.

On Friday, an upper-level trough over the northeast Pacific
will progress toward the Pacific Northwest, bringing slightly
cooler temperatures, increased cloud cover, and increasing
chances of precipitation. Guidance has this trough swinging
inland by Friday night into Saturday. The southerly flow in the
upper-level pattern will bring an increase to for thunderstorm
chances, primarily for the Cascades. The southerly flow aloft
will bring increased moisture and instability, vorticity from
the upper-level trough will also provide the necessary forcing
for convection. Thus resulting in a 15-20% chance for
thunderstorms along the Cascades starting early Friday evening
through Saturday morning.

The latest guidance has precipitation chances beginning over
the Cascades after 5 PM Friday at 20-35% chances, with chances
of precipitation spreading west of the Cascades after 11 PM
Friday. Precipitation chances continue into Saturday morning,
mainly along and north of the OR/WA border. It will be important
to monitor the weather if you have outdoor plans Friday afternoon.

Ensemble guidance continues to show the upper-level trough
moving further into the Pacific Northwest Saturday. As the
associated surface front moves through, will see winds shift and
come out of the west/southwest. Winds will increase through
west to east aligned mountain gaps, especially through the
Central Columbia River Gorge into Hood River Valley where winds
could gust approaching 35 mph. There is also a 40-60% chance
for at least isolated gusts exceeding 40 mph for these areas,
especially for higher terrain and exposed ridgetops. Stronger
onshore flow across the region will support much cooler
temperatures on Saturday with afternoon highs peaking in the
upper 70s.

Sunday into early next week, most ensemble members suggest a
return of zonal flow as the trough moves northeast into
eastern Washington and Canada. As a result, expect temperatures
to gradually cool into the low to mid 80s. Guidance also
indicates another upper-level trough dropping down from the Gulf
of Alaska and approaching British Columbia early next week,
potentially impacting the Pacific NW by mid-week. At this
point, there still remains high uncertainty with the exact
magnitude and placement of the trough next week. However, this
would suggest that onshore flow continues across the region
resulting in seasonable temperatures for late August. -42

&&

.AVIATION...Through 06z Saturday...Marine stratus remains
entrenched along the coast, yielding high confidence in
continued LIFR cigs through at least midday Friday. Restricted
vis is also likely overnight, with increasing chances of
IFR/LIFR vis after 09-12z Fri. Any lifting to IFR cigs Friday
afternoon will be brief, with 30-50% chances for LIFR cigs to
instead persist. Inland, VFR conditions are likely through the
period as low clouds are generally not expected to penetrate
into the I-5 corridor. The most likely terminals to see MVFR
cigs are KEUG (25-35% chance after 12z Fri) and KPDX/KTTD
(15-25% chance after 12z Fri). Otherwise, increasing coverage of
mid to high clouds at or above 15-25 kft is expected through
much of the period. Light south to southwest winds expected
across the airspace, rising to 5-10 kt after 18-21z Fri.

KPDX AND APPROACHES...VFR conditions very likely (85% chance) to
prevail throughout the period beneath increasing mid to high
clouds at or above 15-25 kft. Low chances (15%) for MVFR cigs
from 12-18z Fri if low stratus coverage is higher than expected.
Light west winds early will back out of the south-southwest by
midday Friday, but remain at or below 5 kt. -36

&&

.MARINE...High pressure continues to support northerly winds
across the waters today with gusts remaining well below 20 kt.
Winds over the waters then shift south to southwest on Friday as
a low pressure system moves over the northeast Pacific. As the
surface front continues to move through Saturday, there is a
40-70% chance for maximum wind gusts to exceed 21 kt for the
waters north of Cape Foulweather, including the Columbia River
Bar. For the rest of the waters, chances are 15-30%.

High pressure and northerly winds return by Sunday, with a 30-50%
chance for northerly wind gusts to exceed 21 kts in the late
afternoon and evening hours, with the highest chances south of
Cape Falcon. Seas of 4-6 ft persist through the period. -12/10

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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