Mt. Bachelor

000
FXUS66 KPQR 151745 AAA
AFDPQR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
1045 AM PDT Tue Sep 15 2026

Updated Aviation discussion

.SYNOPSIS...A weak trough will bring increasing clouds and a 
few light showers to the higher terrain today, with seasonably 
cool temperatures continuing. Warmer and drier conditions return
Wednesday and Thursday as easterly flow develops, followed by 
renewed uncertainty in temperatures Friday through the weekend.

.DISCUSSION...Now through Sunday...The weather pattern will 
undergo a fairly noticeable transition over the next couple of 
days. For today, a weak upper-level trough will move across the 
Pacific Northwest while moisture remains limited. Increasing mid
and high level clouds overnight will likely be followed by 
areas of low clouds and patchy fog in the interior valleys this 
morning. Some cloud cover should persist into the afternoon, 
keeping temperatures in the upper 60s to low 70s across the 
interior and in the 60s along the coast. Despite the passage of 
the trough, measurable precipitation is unlikely for most 
locations. The best chances, around 30-50%, will be confined to 
the North Oregon Coast Range, Willapa Hills and Cascade crest, 
with probabilities around 5-15% elsewhere.

The trough will shift southward tonight into Wednesday as 
ridging strengthens offshore and begins to build into the 
Pacific Northwest. This will mark the start of a much warmer 
pattern, with interior highs climbing into the upper 70s to low 
80s Wednesday. A developing thermal trough along the coast and 
Cascade foothills will also turn the low-level flow offshore, 
resulting in increasing easterly winds through the Columbia 
River Gorge and other east-west oriented terrain gaps. Pressure 
gradients between KTTD and KDLS are expected to fall into the -1
to -3 mb range, supporting gusts around 20-25 mph in the Gorge 
and locally breezier conditions over exposed terrain and 
ridgetops. The central and southern Willamette Valley should 
also become breezy as winds turn more northerly. There is a 
30-50% chance of gusts exceeding 30 mph in the Gorge Wednesday, 
with probabilities around 5-15% across the central and southern 
Valley. Despite the warmer temperatures and increasing winds, 
afternoon humidity should remain above 30%, keeping fire-weather
concerns minimal.

Thursday currently appears to be the warmest day of the week. 
Weak offshore flow will continue through the morning, with 
moderate to high confidence for interior temperatures reaching 
the low 80s. The thermal trough should then weaken Thursday 
afternoon, allowing onshore flow to return and limiting further 
warming. Meanwhile, the upper-level trough will shift east 
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.

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 with above-
seasonal-average temperatures. ~12


&&

.AVIATION...Through 18Z Wednesday...Westerly flow aloft turns
north-northeasterly tonight as an upper level trough drops
southward over the Pacific Northwest. Predominately VFR conditions
are expected to continue as mid to high level clouds drift across
the airspace. Lower VFR stratus is likely along the north Oregon
coast through this afternoon with spotty rain showers possible.
Chances for MVFR CIGs at coastal terminals remain around 20%
through 23z today. Otherwise, expect light winds to become north
to northwest around 4-8 kt through early this evening. 

KPDX AND APPROACHES...VFR conditions expected through the TAF
period, with mid to high level clouds through this evening.
Northwest winds persist at around 3-6 kt. /DH

&&

.MARINE...North to northwest winds continue today 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 at least an 80-90% chance for wind gusts exceeding 21 kt 
south of Cape Falcon. As a result, Small Craft Advisories have 
been issued for the waters south of Cape Falcon from 2 to 11 PM 
Wednesday. Small Craft winds could hold on until 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 Tuesday. Seas then build to around 6 ft on 
Wednesday as northerly winds strengthen. 12/23


&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 2 PM to 11 PM PDT Wednesday for PZZ252-
     253-272-273.
&&

$$

www.weather.gov/portland

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