West Linn, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

719
FXUS66 KPQR 200505
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1005 PM PDT Wed Aug 19 2026

Updated aviation discussion.

&&

.SYNOPSIS...Warm and dry conditions through Thursday. Low
pressure brings chances for showers Friday late afternoon into
Saturday across NW OR and SW WA, with a 15% chance for
thunderstorms over the Cascades and 5-10% chance elsewhere.
Winds out of the north/northwest through Thursday, shifting to
the west/southwest on Friday. Seasonable weather returns Sunday
into early next week.

&&

.DISCUSSION...Wednesday afternoon through Tuesday...Visible
satellite imagery early Wednesday afternoon shows mostly clear
skies across NW OR and SW WA. However, the marine layer will
once again inundate the coast this evening into tomorrow
morning with marine stratus making a run down the Lower Columbia
River. Dry and warm weather continues today and tomorrow as an
upper- level ridge amplifies over the Rockies and Great Basin.
Expect high temperatures near or slightly above average for this
time of year, with mid 80s this afternoon across inland valleys
and 60s along the coast. Highs for inland valleys increase
slightly on Thursday into the upper 80s as the upper ridge
reaches its peak strength. Onshore flow continues as broad
upper-level troughing sits over the northeast Pacific with light
winds from the north/northwest.

On Friday, the aforementioned trough over the northeast Pacific
will progress toward the Pacific Northwest, bringing slightly
cooler temperatures, increased cloud cover, and increasing
chances of precipitation. Quite a bit of uncertainty remains
with the exact location of the trough as it moves toward the
area, leading to uncertainty in timing and location of
precipitation over NW OR and SW WA. One note is that this
upper- level pattern on Friday looks like a typical set-up for
thunderstorm chances, at least over the Cascades. Southerly flow
aloft will bring increased moisture and instability into the
mid-levels of the atmosphere (5-10 kft). Vorticity from the
upper-level trough will also provide the necessary forcing for
convection. However, due to the previously mentioned
uncertainty, the timing and location of where vorticity sets up
will really determine if thunderstorms actually occur. The
latest guidance has shifted the precipitation chances to begin
over the Cascades late on Friday afternoon at 25-45% chances,
with 20-30% 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.
Have included a 15% chance of thunderstorms across the Cascades,
but uncertainty is too high for those chances to extend west.
PWATs and RH increase significantly with this moisture, so if
thunderstorms do form, fire concerns are on the lower side. Of
course, any lightning that strikes outside of areas that have
received rain could cause fire starts. It will be important to
monitor the weather if you have outdoor plans Friday afternoon.

Ensemble guidance shows the upper-level trough moving into the
Pacific Northwest on 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 to 25-35
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.

Sunday into early next week, the trough moves northeast into
eastern WA and Canada, and most ensemble members suggest a
return of zonal flow. This will allow for temperatures to rise
back toward near normal, in the low to mid 80s for inland
valleys, with the continuation of onshore flow. Guidance
indicates another upper- level trough dropping down from the
Gulf of Alaska and approaching British Columbia early in the
week, potentially impacting the Pacific NW by midweek. 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. -03/10

&&

.AVIATION...Through 06z Friday...A typical pattern of marine
stratus pushing inland overnight is expected. Along the coast,
satellite imagery and terminal observations already show
widespread low clouds resulting in IFR/LIFR cigs, which will,
with high confidence, continue through at least 18z Fri before
any marginal improvements to MVFR/VFR. Confidence is lower in
the inland penetration of low clouds overnight. Terminals along
the Lower Columbia River (KKLS, KSPB) and into the Portland area
(KPDX, KTTD) will have the highest chances, 40-60%, of low-end
MVFR cigs below 2 kft between 12-18z Fri. Chances for IFR cigs
are not much lower: 20-40%. Within the Willamette Valley, the
likelihood of MVFR cigs is lower, 20-40%, with prevailing VFR
conditions favored. Any low clouds will tend to mix out by
16-18z Fri. Diurnal winds will rise out of the north to
northwest at 5-10 kt by Friday afternoon.

KPDX AND APPROACHES...VFR conditions favored through at least
12z Fri before chances for MVFR/IFR cigs increase as marine
stratus penetrates inland along the Columbia River. Any cigs
will likely be at 2 kft or lower, with nearly 50% chances for
MVFR cigs and 20% for IFR. Any low clouds will tend to mix out
by 16-18z Fri. Northwest winds ease below 3 kt tonight, then
rise to around 5 kt Friday afternoon. -36

&&

.MARINE...High pressure will continue to support northerly
winds across the waters through Thursday with gusts remaining
below 20 kt. Friday to Saturday, weak low pressure moving over
the northeast Pacific will shift winds out of the south to
southwest across the waters. As the surface front moves through
Saturday morning, there is a 30-50% chance for maximum wind
gusts between 21 to 25 kt for the waters north of Cape Falcon,
including the Columbia River Bar. For the rest of the waters,
chances are around 5-10%.

High pressure and northerly winds return by Sunday with a 50-70%
chance for northerly wind gusts exceeding 21 kts in the afternoon
and evening hours with the highest chances south of Cape Falcon.
Seas of 4-6 ft persist through the period. Periods around 12 sec
today may result in a moderate risk for sneaker waves along the
coast. Caution should be used when in or near the water. -03/10

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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