742
FXUS66 KPDT 121133
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
333 AM PST Wed Nov 12 2025

.DISCUSSION...Today, ensemble NWP guidance is in excellent
agreement that a 500-hPa closed low will continue to deepen
offshore in the Pacific, with a surface low spooling up west of
central California. Meanwhile, a 500-hPa ridge will be in place
over the Pacific Northwest, turning flow aloft southwesterly.
Moisture transport into the region is leading to extensive
cloudiness, though precipitation across the forecast area is
sparse with only light echoes on radar. Tangible weather resulting
from subsidence under the ridge will be twofold: first, it will
keep an inversion in place over the Columbia Basin, leading to
patchy/areas of fog through the morning hours where light winds
and a sufficiently moist boundary layer are present; second, it
will lead to warm afternoon temperatures where the inversion
breaks, most notably in central and northeast Oregon. On the first
note, a Dense Fog Advisory is in effect for the foothills of the
northern Blue Mountains of Washington until 10 AM PST where
visibility as low as one-quarter mile has been observed.

Tonight through Thursday, ensemble solutions are nearly unanimous
that the aforementioned surface low will deepen and approach the
OR coast. While there is significantly better agreement with
regard to the location and depth of the surface low relative to
yesterday`s model runs, ensemble members are still displaying a
notable range of solutions. The depth and location of the surface
low tonight through Thursday will modulate the winds across the
region. This pattern generally favors breezy to windy
southeasterly to southerly winds across central Oregon, the Blue
Mountains and their foothills, and the Grande Ronde Valley. That
said, given the aforementioned uncertainty, have low-medium (20-50
percent) confidence in advisory-level winds; the best chance will
be along the northern/western slopes of the Blue Mountains.

Looking ahead to Thursday afternoon through Friday, ensemble
clusters all indicate the main 500-hPa closed low will dive south
off the coast of California while a weaker shortwave trough will
slide across the Pacific Northwest. Aside from widespread
precipitation chances (60-95 PoPs for the mountains, and 40-80
PoPs for the lower elevations), the passage of the shortwave will
drive breezy winds across the region. Confidence is quite low
(10-40 percent) in winds reaching advisory levels, but ensemble
solutions are displaying a wide range of wind gust potential so
will need to keep an eye on how the pattern evolves should one of
the windier solutions materialize.

Quasi-zonal flow aloft is then very likely (all ensemble clusters
depict this solution) Saturday as the shortwave exits and a low-
amplitude 500-hPa ridge moves overhead. Aside from light
precipitation (a couple hundredths to a few tenths of an inch)
for the Cascades and northern Blues, dry conditions are forecast.

Sunday, all ensemble clusters show some flavor of a 500-hPa
shortwave trough approaching the West Coast, although significant
differences in timing are apparent among ensemble clusters. The
vast majority (85 percent) of ensemble members then show a 500-hPa
shortwave trough of varying amplitude over the Pacific Northwest
Monday; this scenario would lead to cool, wet weather across the
Pacific Northwest. The alternate scenario depicts a closed low at
500 hPa off the coast of California; this scenario would be dry
for the Pacific Northwest.

&&

.AVIATION...12z TAFs...Variable conditions persist for PDT and ALW
due to low clouds and fog, while all other sites are expected to be
VFR during the period with bkn-ovc mid-level cigs. Forecast
confidence related to when PDT and ALW will improve this morning is
moderate (40-50%), as an oncoming weather system is expected to
bring warmer air into the forecast area and potentially lift cigs,
however PDT and ALW in particular are known to have low cigs be
stubborn to mix out this time of year. Generally left IFR or worse
conditions in place for both sites through 18z, with MVFR cigs
persisting into the afternoon. Otherwise, expect light winds less
than 10 kts, mainly terrain-driven. 74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  56  41  62  42 /  10  10  50  70
ALW  55  44  61  46 /  10  10  60  80
PSC  53  37  55  42 /   0  10  50  50
YKM  54  39  55  38 /  10  20  80  60
HRI  54  39  57  43 /  10  10  50  60
ELN  51  37  51  35 /  20  30  90  70
RDM  64  44  65  36 /   0  30  40  40
LGD  64  46  64  41 /   0   0  50  80
GCD  67  46  66  42 /   0  10  50  60
DLS  57  44  57  44 /  10  30  90  80

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Dense Fog Advisory until 10 AM PST this morning for WAZ029.

&&

$$

DISCUSSION...86
AVIATION...74