930
FXUS66 KPDT 091742
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
942 AM PST Sun Nov 9 2025

Updated Aviation Discussion

.AVIATION...18Z TAFs...Mostly VFR conditions expected through the
period. Low and patchy fog developed overnight and lead to less
than IFR conditions developing at site PDT this morning, with fog
staying west of site ALW and east of site PSC. Fog is lifting in
these areas as of writing this. A weak system moving into the
region tonight will keep chances of fog low (<15%) across much of
the area, with about a 15-30% chance of MVFR CIGs developing at
site DLS, with less than 15% chance elsewhere. Otherwise, CIGs
will generally remain above 15kft AGL through tomorrow morning.
Winds will be light, 12kts or less, through the period. Lawhorn/82


&&

.PREV DISCUSSION... /issued 320 AM PST Sun Nov 9 2025/

DISCUSSION...

Key Messages:

1. Breezy winds today through Monday morning.

2. Mountain showers Monday, widespread late Wednesday.

3. Pass level snowfall Thursday through Saturday.

Current radar and infrared satellite imagery shows dry conditions
under mostly clear to partly cloudy skies as some high to mid-
level clouds move in from the west. This is in response to an
upper level ridge that is currently centered over the area, which
will begin to shift east and flatten this afternoon and evening.
Due to the eastward shift of the upper level ridge, surface high
pressure will build over south-central Idaho and allow a pressure
gradient to develop over the Blue Mountains. This gradient will
bring breezy winds across the Blue Mountains, Central Oregon, and
the Grande Ronde Valley. Highest winds are expected across the
Grande Ronde Valley, specifically Ladd and Pyles Canyons as
sustained south winds of 20-30 mph with gusts up to 40 mph will be
possible today through Monday morning. Wind gusts at the Charles
Reynolds rest area have already reached 32 mph, with winds
expected to peak between 7 AM and 3 PM today before a second peak
occurs between 5 PM and 11 PM this evening. The pressure gradient
will slowly slacken overnight through Monday morning, but
elevated winds are still anticipated. Confidence in these wind
values and timing is high (80-90%) as the SREF and NAM advertise a
pressure gradient of 6.3-6.8 mb and the HREF highlights a 55-65%
chance of wind gusts reaching 40 mph or greater over Ladd and
Pyles Canyons. Other locations will experience lower winds, with
the Blue Mountains likely receiving sustained winds of around 20
mph and gusts up to 35 mph and Central Oregon with sustained winds
of 15-20 mph and gusts up to 30 mph.

The weak, incoming upper level shortwave that will be enhancing
the pressure gradient across the Blue Mountain today and early
Monday, will also bring the potential for mountain showers along
the Cascades (primarily Washington). Snow levels will be quite
high (8000-9000 feet), so the majority of precipitation will be
liquid aside from high terrain. Minimal rain amounts of around
0.10" are expected along the Washington crest, with only a trace
likely to reach into the Oregon Cascades. A transient ridge will
quickly pass through the area Tuesday ahead of a much more
substantial system that will impact the Pacific Northwest through
the remainder of the week. Ensemble guidance is in good agreement
with the mid-to late week system, but differences in strength and
timing still exist. Current guidance suggests showers will begin
along the Cascades by late Wednesday morning before extending
along the east slopes by the afternoon and into Central Oregon and
the Columbia Basin overnight into Thursday morning. However, 59%
of ensemble members hint at a delayed arrival and a deeper, less
broad system. This scenario would bring the majority of rainfall
to lower elevations on Thursday, with rain amounts of 0.15-0.25"
across the Blue Mountain foothills, Grande Ronde Valley and John
Day Basin; and 0.05-0.15" of rainfall through the Lower Columbia
Basin and Central Oregon. Showers are expected to become more
confined to the Cascade and Blue Mountains into Friday morning as
a weak transient ridge moves onshore ahead of the next system
expected late in the weekend.

Snow levels will be dropping from 6500-7000 feet late Wednesday
night to 4000-5000 feet Thursday evening associated with a cold
front passage. This will allow for pass-level snow to occur
Thursday and Friday, with light accumulations potentially on
Saturday. Possible snow accumulations across White and Santiam
passes look to reach between 1-3 inches Thursday, 2-5 inches
Friday, and 1-3 inches on Saturday. These amounts would result in
advisory-level snow amounts over Santiam Pass, with a Thursday-
Friday total of 6-7 inches. However, the later and less broad
scenario is not ideal for snowfall as a more southerly flow aloft
will attribute to higher snow levels and less snow accumulations.
This is reflected in NBM guidance, which suggests a 50-60% chance
of Santiam Pass receiving advisory-level snowfall (5 inches or
more) Thursday through Friday. Higher terrain over the Cascades
and Elkhorns could receive up to a foot of snowfall Thursday
through Saturday, with high elevations of the Blue Mountains
picking up 1-4 inches of snow. 75



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  54  37  60  41 /   0   0   0   0
ALW  53  41  59  45 /   0   0   0  10
PSC  52  36  56  35 /   0   0   0   0
YKM  55  37  58  33 /   0   0   0   0
HRI  53  37  58  39 /   0   0   0   0
ELN  51  35  55  34 /   0   0  10   0
RDM  64  36  66  33 /   0   0   0   0
LGD  60  43  63  40 /   0   0   0  10
GCD  66  39  68  37 /   0   0   0   0
DLS  55  41  61  43 /   0   0  10  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

DISCUSSION...75
AVIATION...82