165
FXUS66 KPQR 160519 AAB
AFDPQR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
1018 PM PDT Tue Sep 15 2026

Updated aviation discussion.

.SYNOPSIS...A weak trough will continue to bring scattered clouds
and cool weather this afternoon. Warmer and drier conditions
return Wednesday and Thursday as easterly winds develop across the
Columbia Gorge, Cascades, and Coast Range with northerly winds
along the I-5 corridor. Winds from the west return Thursday
afternoon. Dry and warm conditions continue Friday through the
weekend, with potential for cooler weather next week.

&&

.SHORT TERM...Today through Thursday night...Satellite imagery
as of early Tuesday afternoon depicts widespread high-level
clouds across northwest Oregon and southwest Washington as a
weak upper-level trough swings through the region. Radar imagery
is also showing some scattered light showers, however, surface
observations have shown no measurable precipitation so far. In
addition, model soundings are showing a drier low-level
atmosphere, which suggests that these showers could be falling
as virga. Therefore, hourly chances for precipitation for the
rest of the day remain below 10% for most locations except
20-40% along the crest of the Cascades. Expect high temperatures
this afternoon to peak in the upper 60s across interior valleys
and low to mid 60s along the coast due to the cloud cover.

The aforementioned trough will shift southward into northern
California tonight into Wednesday and turn into a closed low as
upper-level ridging strengthens offshore. Thermal troughs will
develop along the coast and Cascade foothills, supporting  a
return of winds from the east/northeast through the Columbia
River Gorge and downsloping off the Cascades and Coast Range.
These downsloping winds will support drier and warmer air along
the coast and I-5 corridor, with high temperatures rebounding
into the upper 70s to low 80s across interior valleys and low
70s along the coast.

Ensemble guidance continues to suggest pressure gradients
between KTTD and KDLS are expected to fall into the -1 to -3 mb
range, supporting gusts around 20-30 mph through the Gorge and
east-west aligned gaps through the Cascades, with locally breezier
gusts up to 40 mph for exposed ridgetops. There is only a 5-15%
chance for wind gusts exceeding 40 mph for these ridgetops.
Meanwhile, the central and southern Willamette Valley will also
become breezy as winds turn more northerly into the I-5
corridor. Wind gusts across the Valley are expected to peak
around 20-25 mph, with a 10% chance for gusts exceeding 30 mph.
While these easterly winds. Despite the warmer temperatures and
increasing easterly winds, afternoon humidity should remain
above 30% due to recent moisture, keeping concerns for rapid
fire spread minimal.

Thursday remains the warmest day of the week. Weak offshore flow
will continue through the morning, with high confidence for
interior valley highs peaking in the low 80s. Thermal troughing
should break down Thursday afternoon, allowing onshore flow to
return. Meanwhile, the upper-level low over northern California
will shift northeastward toward the Great Basin. Some wrap-
around moisture could produce a 5-10% chance of thunderstorms
along the crest of the Lane County Cascades Thursday, while the
remainder of the forecast area remains dry and outside the
thunderstorm threat. SPC has included a portion of the Lane
County Cascades in a general thunderstorm risk, so this
potential will need to be monitored as Thursday approaches. -10/12

&&

.LONG TERM...Friday through Monday...The forecast becomes more
uncertain Friday through the weekend as ensemble guidance
diverges on how quickly the upper-level pattern evolves. Roughly
half of the guidance maintains weak troughing over the Great
Basin, which would keep temperatures closer to the low 70s,
while the other half favors stronger ridging over the Pacific
Northwest and warmer temperatures potentially reaching the mid
80s. Thus, there is still a fairly broad range in possible
temperatures late in the week, but the overall signal continues
to favor dry weather. By early next week (Monday), most ensemble
members begin to hint at an upper- level trough dropping down
from the Gulf of Alaska. The impacts of this trough remain
uncertain for the Pacific Northwest at this time, but it would
suggest a continuation of onshore flow and potentially cooler
temperatures next week. -10/12

&&

.AVIATION...Through 06Z Thursday...At 0515Z Wednesday, VFR flight
conditions were being observed at all TAF sites under mostly clear
skies. A few clouds remain around 6000 ft, however these clouds
are expected to dissipate later tonight. Expect mostly clear
skies thereafter for the remainder of the 06Z TAF period,
resulting in continued VFR conditions.

Offshore winds begin to develop at the surface beginning early
Wednesday morning. By Wednesday afternoon, east to northeast
winds will increase at KTTD, KUAO, KHIO, and KPDX with gusts as
high as 20 kt. North winds will increase from KSLE to KEUG and at
KONP Wednesday afternoon with gusts as high as 25 kt. North winds
will be weakest at KAST. It appears winds will weaken in strength
by 03Z Thursday.

KPDX AND APPROACHES...VFR conditions expected through the TAF
period with mostly clear skies. Northwest winds around 6-7 kt
this evening will become northerly around 10 kt by 18Z Wednesday.
By approximately 20-21Z Wednesday, winds should become
northeasterly with wind gusts up to 20 kt. The exact timing winds
will transition from northerly to northeasterly is unclear, and
may occur anytime between 18-22Z Wednesday. Winds should weaken
fairly quickly between 02-03Z Thursday. -23

&&

.MARINE...North winds will continue tonight as high pressure
builds offshore. A strengthening thermal trough along the coast is
expected to increase pressure gradients across the coastal waters
on Wednesday, increasing northerlies to 15-20 kt with gusts up to
25 kt south of Cape Falcon. Isolated gusts as high as 30 kt are
possible over the southern outer waters to the south of Cape
Foulweather, beyond 10 NM offshore. Gusts are now expected to
approach 20-25 kt by late Wednesday morning for the central and
southern offshore waters, and by Noon over the inner waters. As a
result, Small Craft Advisories have been extended in time to begin
at 11 AM Wednesday and end at 11 PM Wednesday. Small Craft winds
could hold on until as late as 2 AM Thursday but confidence
remains low at this time.

Winds are likely to ease later in the week as low pressure drifts
offshore. A persistent northwest swell around 4 to 5 ft at 7 to 8
seconds is expected to continue through tonight. Seas then build
to around 6 ft on Wednesday as northerly winds strengthen.
Northerlies strengthen again over the weekend, with around a
40-50% chance of wind gusts exceeding 21 kt. -23/DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 11 AM to 11 PM PDT Wednesday for
     PZZ252-253-272-273.
&&

$$

www.weather.gov/portland

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