875
FXUS66 KPDT 111423
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
623 AM PST Tue Nov 11 2025

.UPDATE...Areas of dense fog have expanded across much of the
Yakima Valley and lower Columbia Basin of Washington, so have
issued a Dense Fog Advisory for those zones, valid until 1000 PST.
Visibilities are expected to improve by 1000-1100 PST.

&&

.PREV DISCUSSION... /issued 332 AM PST Tue Nov 11 2025/

DISCUSSION...Satellite imagery reveals zonal flow aloft over the
forecast area, with cirrus blanketing the majority of south-
central to southeast Washington and north-central to northeast
Oregon. Beneath the cirrus, some lower clouds are present, but
hidden from view. At the surface cold pooling is evident,
extending from the the lower Columbia Basin of Oregon north
through the lower elevations of south-central Washington. Fog,
locally dense with visibility of one-quarter mile or less, has
formed in the cool, moist air mass. Have issued a Special Weather
Statement for the patchy dense fog, which is expected to persist
in portions of the lower Columbia Basin of Washington and Yakima
Valley through early to mid-morning. Farther south, a milder, less
saturated air mass remains in place across the Blue Mountain
foothills and much of the remainder of central to eastern Oregon.

Ensemble NWP guidance is in excellent agreement that a couple
vort lobes in the vicinity of the Gulf of Alaska will dive
southeast today through Wednesday and carve out a deep 500-hPa
trough/closed low offshore. Meanwhile, a 500-hPa ridge will build
over the Rockies and into the Pacific Northwest, turning flow
aloft southwesterly. Currently, not anticipating any noteworthy
weather until Wednesday night and Thursday morning when the
aforementioned closed low approaches the OR coast. While there is
significantly better agreement in pattern details relative to
yesterday`s model runs, ensemble members are still displaying a
notable range of solutions with regard to the formation and
evolution of a surface low and cold front. The pattern generally
favors breezy to windy southeasterly to southerly winds across
central Oregon, the Blue Mountains and their foothills, and the
Grande Ronde Valley. Currently, have low-medium (20-50 percent)
confidence in advisory-level winds Wednesday night and Thursday
for the aforementioned zones.

Looking ahead, ensemble clusters all indicate the main 500-hPa
closed low will dive south into California and the Southwest while
a weaker shortwave trough will slide across the Pacific Northwest
late Thursday through Friday. Northwesterly to westerly flow
aloft is then favored through Saturday as the shortwave exits and
a brief ridge moves overhead. By Sunday, all ensemble clusters
show some flavor of a shortwave trough approaching the West Coast.

AVIATION...12Z TAFs...Predominantly VFR conditions are forecast
for the next 24 hours. The main exceptions are at DLS where low
stratus may (50 percent confidence) bring IFR CIGs through this
morning, and at PSC where confidence is medium-high (50-80
percent) in periods of dense fog through mid-morning. Otherwise,
mostly middle to high cloud and light winds (10 kts or less) are
anticipated across TAF sites.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  57  39  56  41 /   0  10   0  20
ALW  57  43  55  45 /   0  10  10  20
PSC  53  38  53  39 /   0  10   0  10
YKM  55  39  54  39 /   0  20  10  40
HRI  55  40  53  41 /   0  10   0  20
ELN  51  36  50  37 /   0  30  20  50
RDM  62  41  64  43 /   0   0   0  30
LGD  63  45  62  46 /   0   0   0  10
GCD  67  44  66  47 /   0   0   0  30
DLS  58  44  57  45 /  10  20  20  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Dense Fog Advisory until 10 AM PST this morning for WAZ027-028.

&&

$$

UPDATE...86
DISCUSSION...86
AVIATION...86