213
FXUS66 KPDT 011220
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
420 AM PST Sun Nov 1 2026

.KEY MESSAGES...

- Areas of dense fog and freezing fog today.

- Near- to below-normal temperatures into next week.

- Low chance (30% or less, except for freeze-prone areas) of a
  season-ending freeze for the eastern Columbia River Gorge
  Monday.

&&

.DISCUSSION...
Water vapor imagery shows a splitting trough over the forecast
area, with the main circulation centers tracking over northern
California and the Canadian Rockies. Nighttime microphysics
imagery reveals middle and high cloud cover across far eastern
Oregon and Washington, while much of central to eastern Oregon
and southeast Washington are under a blanket of low stratus.
Elsewhere, mostly clear skies are noted over south-central
Washington. Radar reveals isolated showers over the Columbia
Plateau, mainly near and north of Walla Walla. At the surface,
most valley locations are nearly saturated at around 90-100%
RH, and additional fog formation remains a concern for early
morning. Have issued a Dense Fog Advisory for the northern and
southern Blue Mountains where low stratus is intersecting the
terrain and creating near-zero visibility in places; this low
visibility is affecting routes over the Blue Mountains including
but not limited to Interstate 84, Highway 395, and Highway 204.
Elsewhere, patchy to areas of dense fog and dense freezing fog
are present in central Oregon; have issued a Special Weather
Statement for this fog, though if it becomes more widespread, an
advisory may be needed.

Ensemble guidance indicates the trough will exit to the east
this evening, and an amplified upper-level ridge will build in
from the Pacific through Monday. Given clearing skies and dry
conditions, this presents the best chance, albeit low at 30% or
less, of a season-ending freeze for the eastern Columbia River
Gorge in the next week. Freeze-prone portions of the Gorge do
have somewhat higher chances of freezing (locally in excess of
50%), but at this time confidence remains too low to issue any
watches.

Uncertainty in the 500-hPa pattern then grows Tuesday through
the remainder of the week. Ensemble clusters show a range of
solutions regarding a compact closed low Tuesday into Wednesday.
The majority of solutions (~80%) take the low too far south
across southern Oregon or northern California to produce
significant precipitation for our forecast area, and mostly dry
conditions (PoPs of 20% or less) are forecast to continue until
late Wednesday when ensemble guidance hints at the return of
some more active weather in the form of a shortwave trough. By
Friday and Saturday, ensemble clusters are showing medium
potential (roughly 50% chance) for a return to a wet pattern.
NBM probabilities indicate a low-medium (20-60%) chance for at
least 0.50" of precipitation across the Cascades and northern
Blue Mountains during the Friday through Saturday period;
highest chances are for the Washington Cascades. That said, the
alternate scenario is for an upper-level ridge to be overhead
with precipitation displaced to the northwest of our forecast
area.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Fog and low stratus remain the primary drivers of aviation
concerns through the period. Low stratus at BDN/RDM is forecast
to keep at least IFR conditions in place through morning, while
fog and/or low stratus at PDT/ALW/PSC will present at least
periodic MVFR or lower CIGs/VSBYs. Showers in the vicinity of
ALW are expected to taper off through morning. Clearing skies
are forecast by this evening for all sites, though there is some
potential for low stratus to remain through the day (30%
confidence or less). Winds of 12 kts or less are anticipated.

&&

.Preliminary Point Temps/PoPs...
PDT  48  31  57  36 /  20   0   0   0
ALW  49  35  56  39 /  20   0   0   0
PSC  54  30  56  34 /  10   0   0   0
YKM  58  29  55  37 /   0   0   0   0
HRI  53  31  56  34 /  10   0   0   0
ELN  55  25  52  30 /   0   0   0   0
RDM  49  21  57  28 /  10   0   0   0
LGD  48  29  56  35 /  30   0   0   0
GCD  48  30  58  35 /  10   0   0   0
DLS  57  33  57  40 /   0   0   0  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...None.
OR...Dense Fog Advisory until noon PST today for ORZ502-503.

&&

$$

DISCUSSION...86
AVIATION...86