478
FXUS66 KPDT 021208
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
408 AM PST Mon Nov 2 2026

.KEY MESSAGES...

- Patchy dense freezing fog this morning, mainly for the Blue
  Mountains region and fog-prone valleys within the Columbia
  Basin.

- Near-normal temperatures and mostly dry conditions until a
  weak weather system arrives late Wednesday.

&&

.DISCUSSION...
GOES-18 water vapor imagery shows an amplified upper-level
ridge extending from California northeast through the Canadian
Rockies. Upstream in the Pacific, a low-pressure system is
developing in the vicinity of 39N, 142W. Nighttime microphysics
imagery reveals mostly clear skies across the forecast area,
albeit with low stratus and/or fog in portions of the eastern
Columbia River Gorge, lower Columbia Basin, Blue Mountains, and
cold mountain basins. At the surface, most valley/basin
locations are nearly saturated at around 90-100% RH, and
additional fog formation remains a concern for early morning.
Have held off on any headlines due to the patchy nature, but
will continue to monitor the situation.

The aforementioned area of low pressure is expected (90%
confidence) to develop into a closed low by Tuesday, eventually
moving inland over southern Oregon or northern California by
late Tuesday. Ensemble guidance suggests the low will be too far
south to produce significant precipitation for our forecast
area, and mostly dry conditions (PoPs of 20% or less) are
forecast to continue until late Wednesday into Thursday when
ensemble guidance highlights the arrival of a shortwave trough.
Clusters of ensemble solutions continue to indicate significant
spread in how much precipitation will accompany the shortwave;
roughly one-third of members place noteworthy precipitation
across the forecast area, while the remainder keep
precipitation confined to the Cascade crest.

By Friday, ensemble clusters are showing medium potential (~65%)
of wet weather for the Washington Cascades, with significantly
lower chances (~30%) for wet weather east of the Cascades.
Ensemble guidance is trending towards mostly dry solutions
(75-85%) by Saturday with an upper-level ridge overhead and
precipitation displaced to the northwest of our forecast area.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Predominantly VFR conditions are forecast at TAF sites over the
next 24 hours, with the exception of some sub-VFR conditions
this morning. Highest confidence (40-80%) in sub-VFR conditions
will revolve around ongoing or forecast low stratus and fog this
morning at DLS/PSC. A ribbon of stratus has been developing in
the eastern Columbia River Gorge early this morning, and while
DLS has yet to report a ceiling associated with it, confidence
was high enough in temporary MVFR CIGs to include a TEMPO group.
At PSC, anticipating some temporary VSBY reductions as patchy
fog has been developing in the Columbia Basin. Otherwise, winds
of 12 kts or less are forecast, and mid/high cloud cover will
increase through the period as a weather system approaches from
the Pacific. While light precipitation cannot be entirely ruled
out later this evening into tonight, chances are too low (15% or
less) to include a mention in the 12Z TAFs.

&&

.Preliminary Point Temps/PoPs...
PDT  58  36  51  31 /   0   0  10   0
ALW  57  39  52  35 /   0   0  10   0
PSC  58  38  54  31 /   0   0   0   0
YKM  55  39  57  30 /   0   0  10   0
HRI  58  38  53  30 /   0   0  10   0
ELN  53  34  51  27 /   0  10  10   0
RDM  59  31  51  23 /   0   0   0   0
LGD  53  37  57  31 /   0   0   0   0
GCD  57  36  57  31 /   0   0  10   0
DLS  59  41  57  35 /   0  10  10   0

&&

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

&&

$$

DISCUSSION...86
AVIATION...86