631
FXUS66 KPDT 220544
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
944 PM PST Fri Nov 21 2025

.Updated for Aviation

.AVIATION...
06Z TAFS....Conditions were generally VFR across the region, but
PSC had LIFR in fog and stratus. The expectation is that most, if
not all of the TAF sites will see fog and/or stratus develop
overnight or towards morning and remain through the morning hours
before dissipating. Conditions will decrease to MVFR if not lower,
before improving to VFR again. Winds are expected to be light.



&&

.PREV DISCUSSION... /issued 239 PM PST Fri Nov 21 2025/

DISCUSSION...

Key Messages:

1. Patchy fog developing overnight.

2. Widespread precipitation chances Sunday.

3. Showers return Tuesday through Thursday - lower elevation snow?

Current radar and visible satellite imagery shows dry conditions
under mostly sunny skies. This is in response to an upper level
ridge and surface high pressure that has warmed temperatures up
slightly today and Saturday ahead of the next system that will
impact our area on Sunday. The abundant high pressure will allow
for areas of fog to again develop tonight into Saturday morning
for areas of Yakima, Hermiston, and the Tri-Cities. A Freezing Fog
Advisory was issued this morning across the Lower Columbia Basin
of Washington and Oregon, which is expected to repeat Saturday
morning. The chance of visibilities of one half mile or less via
the HREF are as followed: 35% for Sunnyside, 20% over Tri-Cities,
13% for Hermiston, and 10% through Yakima. Even though these
probabilities do seem low, the probabilities for these conditions
this morning were 25-30%. Morning temperatures in these areas will
again dip below freezing, so freezing fog will again be a concern.
Low visibilities will again be possible early Sunday morning for
the Hermiston and Tri-Cities areas, but an incoming system will
limit overall coverage. Chances for one half mile visibility or
less is only 10-15% for Tri-Cities and Hermiston Sunday via the
HREF.

Ensembles are in good agreement regarding a shortwave trough
passing through the Pacific Northwest Sunday into Monday, bringing
primarily mountain snowfall and light low elevation rain showers.
Snow levels will be dropping from 5000-6000 feet Sunday morning
to 3500-4500 feet Sunday night, and 2000-3000 feet Monday morning.
Showers will begin along the Cascades Sunday morning before
extending across the Lower Columbia Basin and the northern Blue
Mountains by late morning and persisting through Monday morning.
Snow amounts of 1-3 inches are expected at pass level across the
Cascades and over higher terrain in the northern Blue Mountains.
Rain amounts are expected to reach 0.05-0.15" along the northern
Blue Mountain foothills and the Grande Ronde Valley, with less
than 0.05" likely across lower elevations of the Columbia Basin.
Breezy winds will also accompany this passing system late Sunday
into Monday morning, with sustained west-southwest winds of 15-20
mph and gusts up to 35 mph through the Eastern Gorge, Simcoe
Highlands, Kittitas Valley, and the Blue Mountains/foothills.

A transient upper level ridge moves in Monday to dry conditions
through the afternoon and evening ahead of the next system that
begins with a shortwave Tuesday before a more substantial upper
level trough Wednesday and Thursday. Snow levels will be
increasing through the period, from 3000-4000 feet Tuesday to
4000-5000 feet Wednesday and Thursday. Currently, 70% of ensemble
members suggest a slight chance (10-25%) of measurable snowfall
(0.01" or greater) across lower elevations of the Columbia Basin
Tuesday night into Wednesday morning. Current snow amounts look to
be highest across the Washington Cascades, with 5-9 inches across
White and Snoqualmie Passes Tuesday through Wednesday - which
does meet Winter Weather Advisory criteria. However, confidence is
rather low at this time as the NBM suggests a 30-40% chance of
advisory level snowfall (6 inches or greater) across the
Washington Cascade passes. The northern Blue Mountains are
currently forecast to receive 3-5 inches and the Oregon Cascades
1-2 inches Tuesday through Wednesday. Lower elevations of the
Basin and Central Oregon could pick up 0.10-0.20" of rainfall on
Wednesday, but confidence in these amounts are rather low (30-50%)
at this time. 75

AVIATION...00Z TAFs...All sites will be VFR through this evening.
KDLS/KYKM/KPSC may become MVFR or lower from the fog/mist and low
CIGs thus dropping their VSBYs, respectively. Fog/mist should clear
out later Saturday morning. Otherwise, winds will remain less than
10kts. Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  31  51  34  52 /   0   0   0  30
ALW  36  51  38  52 /   0   0   0  40
PSC  29  47  32  51 /   0   0   0  20
YKM  29  49  34  49 /   0   0   0  30
HRI  29  48  33  51 /   0   0   0  20
ELN  30  48  34  47 /   0   0  10  50
RDM  24  58  28  54 /   0   0   0  10
LGD  30  53  34  51 /   0   0   0  20
GCD  29  56  31  55 /   0   0   0  10
DLS  35  51  39  51 /   0   0   0  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Dense Fog Advisory until 10 AM PST Saturday for WAZ028.

&&

$$

SHORT TERM...75
LONG TERM....97
AVIATION...77