251
FXUS66 KPDT 061108
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
408 AM PDT Mon Oct 6 2025


DISCUSSION...An upper-level ridge of high pressure extends from
the northeastern Pacific Ocean into the Pacific Northwest. Beneath
the ridge, clear skies coupled with predominantly light winds and
a dry air mass (PWATs of 0.25-0.60") will facilitate efficient
radiational cooling. Isolated near-freezing to 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 as well as
Tuesday morning. 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. Freeze Warnings remain in effect until 10 AM for
the aforementioned zones.

By Tuesday, the ridge will flatten as a couple vort lobes drop
south from the Gulf of Alaska and BC and carve out an offshore
closed low. Analysis of ensemble clusters suggests a very high
chance (>90%) that the low will deepen and spin offshore of the
Pacific Northwest Wednesday through Thursday. Any precipitation
associated with the low will likely (75% chance) remain pinned to
the Cascades and their immediate east slopes.

Ensemble clusters indicate the longwave pattern will almost
certainly (>90% chance) become more progressive Friday through
the weekend. While some differences in exact timing are apparent
among ensemble clusters, all ensemble systems track the closed
low inland over the Pacific Northwest Friday through Saturday,
with a second shortwave trough digging southeast out of BC
Saturday through Sunday. The combination of these two systems will
facilitate 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) over the weekend to allow a
medium-high chance (50-80%) of measurable snow in the mountains.

Breezy westerly winds are also forecast Saturday into Sunday.
NBM probabilities suggest a low-medium (30-60%) 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 will prevail through the
forecast period. CIGs will be primarily SKC with variable light
winds at all TAF sites. Bennese/90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  69  40  74  43 /   0   0   0   0
ALW  69  45  74  48 /   0   0   0   0
PSC  70  37  72  40 /   0   0   0   0
YKM  70  41  72  41 /   0   0   0   0
HRI  70  38  73  41 /   0   0   0   0
ELN  69  37  70  38 /   0   0   0   0
RDM  68  31  75  34 /   0   0   0   0
LGD  66  35  72  42 /   0   0   0   0
GCD  68  36  73  38 /   0   0   0   0
DLS  73  44  76  46 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning until 10 AM PDT this morning for ORZ049-050-505-
     511.

WA...None.
&&

$$

SHORT TERM...86
LONG TERM....86
AVIATION...90