084
FXUS66 KPQR 202203
AFDPQR

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

.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.

&&

.AVIATION...Through 00Z Saturday...Marine stratus continues to
flirt with the coastline, bringing conditions bouncing between
MVFR/IFR to the coastal terminals, most notable at KONP.
Confidence for any persistent flight restriction remains low.
Regardless, by 00-03Z Fri, marine stratus will push back into the
coast and bring LIFR/IFR conditions to the coastal terminals
(60-70% chance of LIFR and greater than 80% for IFR conditions).
These deteriorated conditions will persist until at least 18Z Fri
and then possibly improve to IFR/MVFR thereafter. As for the
Willamette Valley, VFR conditions and clear skies will prevail
through the TAF period (with the caveat of a 10-20% chance of
MVFR CIGs between 10-19Z Fri). Otherwise, current west/northwest
winds under 10 kt will shift westerly to southwesterly between
03-12Z Fri (earliest to latest from coast to inland).

KPDX AND APPROACHES...VFR and clear skies will continue through
the TAF period, with a 10-15% chance of MVFR CIGs between 12-18Z
Fri. Northwest winds around 3-6 kt will shift westerly by 12Z
Fri. ~12

&&

.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.

&&

$$

www.weather.gov/portland

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