431
FXUS66 KPDT 071111
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
411 AM PDT Tue Oct 7 2025


DISCUSSION...A flattening upper-level ridge of high pressure is
in place over the Pacific Northwest. Beneath the ridge, clear
skies coupled with predominantly light winds and a dry air mass
(PWATs of 0.25-0.55") will facilitate another night of relatively
efficient radiational cooling. Isolated near-freezing
temperatures are expected (80% confidence) this morning for low-
lying, cold-prone locations within the Yakima and Kittitas
valleys, Columbia Basin, and along the Blue Mountain foothills; no
Freeze Warnings have been issued due to limited spatial extent.
However, have added a mention of frost in the forecast this
morning for the coldest locations. Elsewhere, more widespread sub-
freezing temperatures are expected (80-100% confidence) this
morning for central Oregon, the John Day Basin, and the Grande
Ronde and Wallowa valleys. The aforementioned zones observed their
season-ending freeze last night, so no additional Freeze Warnings
will be issued this season.

Looking ahead, a couple vort lobes are progged to drop south from
the Gulf of Alaska and BC and carve out an offshore closed low
today through Wednesday. Analysis of ensemble clusters suggests a
very high chance (>90%) that the low will then deepen and spin
offshore through Thursday. Relative to last night`s forecast,
precipitation chances (15-45%, highest for the Cascades and east
slopes) for Wednesday night and Thursday have spread eastward to
encompass much of the CWA.

Ensemble clusters indicate the longwave pattern will almost
certainly (>90% chance) become more progressive late Friday
through the weekend. While some differences are evident among
ensemble clusters, all track the closed low inland over the
Pacific Northwest through Saturday, with a second shortwave
trough digging southeast out of BC Saturday through Sunday. The
combination of these two systems will induce medium-high chances
(55-85%) of precipitation for the Cascades and Blues with a low-
medium chance (20-50%) of rain for the lower elevations late
Friday through Sunday. Snow levels will drop sufficiently low (4-5
kft) Saturday night through Sunday to allow a medium-high chance
(50-80%) of measurable snow in the mountains.

Breezy to windy westerly winds are forecast Saturday into Sunday
as the second shortwave tracks across the region. NBM
probabilities suggest a medium-high (40-70%) chance of winds
reaching advisory thresholds, and the ECMWF EFI for wind and wind
gusts ranges from 0.5-0.8 across wind-prone areas of the Columbia
Gorge/Basin and adjoining foothill and valley areas. Plunkett/86

AVIATION...12Z TAFs...VFR conditions to prevail through the
period. There is 30% chance of YKM seeing smoke leading to MVFR
haze impacts in the morning to early afternoon. Winds will be
light, 10 kts or less, and diurnally driven through the period.
Bennese/90



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  74  44  72  41 /   0   0   0  10
ALW  74  49  73  46 /   0   0   0  10
PSC  72  41  73  41 /   0   0   0  10
YKM  72  42  70  43 /   0   0   0  20
HRI  73  42  72  42 /   0   0   0  10
ELN  70  39  66  39 /   0   0   0  30
RDM  75  35  71  34 /   0   0   0  20
LGD  72  42  73  40 /   0   0   0  10
GCD  73  39  76  42 /   0   0   0  10
DLS  77  47  68  46 /   0   0   0  30

&&

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

$$

DISCUSSION...86
AVIATION...90