345
FXUS66 KPDT 240541
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
941 PM PST Sun Nov 23 2025

.UPDATED AVIATION...06Z TAFs...This passing system will continue
bring light rain for KDLS/KPDT/KRDM/KBDN/KALW through this evening
with KPSC joining in around 08Z. In addition to low clouds, this
could also bring KDLS/KPDT/KALW to MVFR overnight (06Z-10Z) with
light rain lingering over KPDT/KALW between 10Z and 13Z (<30%
confidence). Sustained winds of 12-20kts with gusty winds at
20-25kts for all sites may develop overnight into Monday late
morning. Around Monday afternoon, winds should then decrease to
less than 12kts. Feaster/97

&&


.PREV DISCUSSION... /issued 147 PM PST Sun Nov 23 2025/

.DISCUSSION...Snow levels will drop later this afternoon through
tonight as a cold front from the Pacific sweeps across the
region. No winter highlights are in effect, but do have medium-
high confidence (60-80 percent) in one-half inch to two inches of
snow for mountain passes in the Cascades and northern Blue
Mountains. Additionally, breezy to locally windy westerly winds of
15-25 mph accompanied by gusts of 25-40 mph are forecast across
wind-prone portions of the Columbia Plateau with and behind FROPA,
persisting through Monday as a shortwave trough moves overhead.

Tuesday afternoon through Thursday, forecast details are still
fuzzy as ensemble guidance struggles to resolve features of a
progressive weather pattern, including the magnitude and axis of
moisture transport into the Pacific Northwest, focusing mechanisms
for precipitation (fronts, surface lows, etc.), and any wintry
precipitation for the mountains and lowlands. That said, NWP
guidance is presenting a range of solutions that is favorable for
winter weather across portions of our forecast area. Winter
weather conditions are most likely along the Washington Cascades
and their adjacent eastern slopes as well as the Yakima and
Kittitas valleys, with lower chances for the northern Blue
Mountains and Blue Mountain basins such as the Grande Ronde and
Wallowa valleys.

To dive into specifics for Tuesday through Thursday, ensemble
solutions generally drape a warm front over the forecast area by
Tuesday afternoon, with the location presented by members ranging
from north-central Oregon to south-central Washington. Meanwhile,
near- to sub-freezing air at the surface is possible (50-80
percent confidence) across the aforementioned areas of south-
central Washington and northeast Oregon. Solutions then range from
a slow-moving or even quasi-stationary frontal boundary persisting
across the forecast area through Wednesday night to a faster-
moving frontal boundary that pushes into northern Washington
(out of our forecast area) by Wednesday afternoon. Thermodynamic
profiles in NWP guidance are supportive of snow or light freezing
rain where cold air remains trapped, with precipitation type
largely depending on the location of the warm front, warm air
aloft, and surface temperatures.

To better quantify the range of solutions in guidance, one can
look at clusters of ensemble members that present similar
solutions. In this case, examining clusters based on QPF output
indicates roughly 45 percent of ensemble variance can be explained
by location and/or timing differences in the aforementioned warm
front, while an additional 22 percent is driven by the magnitude
of QPF across Washington and far northern Oregon. Moreover, 65
percent of ensemble solutions place the axis of QPF over north-
central Oregon to south-central Washington, while the remaining 35
percent advertise mostly dry conditions for Oregon with the QPF
axis shifted north to Washington.

So will it snow in the lowlands? The NBM suggests a low
probability (5-15 percent) of 1 inch or greater snowfall for the
24-hr period ending 10 AM PST Wednesday for the Yakima, Kittitas,
and Grande Ronde valleys. Based on experience, these probabilities
are likely too low given the synoptic setup, and would
subjectively increase them to 10-50 percent, highest for the
Kittitas Valley. In the eastern half of the Columbia Basin and
farther south into central Oregon, guidance is more confident in a
warmer air mass (south of the warm frontal boundary), resulting
in very low probabilities of measurable snowfall (less than 5
percent). While probabilities from the NBM are still quite low
(up to 10 percent), the synoptic pattern does support some
potential for measurable freezing rain Tuesday night and Wednesday
in sheltered valleys along the east side of the Washington
Cascades, the Grande Ronde Valley, and sheltered locations within
the northern Blue Mountains as warm air overrides colder air at
the surface.

Compared to the lowlands, winter weather is more likely for the
mountain passes, though 48-hr NBM probabilities of advisory-
level snowfall are still just medium (40-50 percent) for the
Washington Cascades including Snoqualmie and White passes with
lower probabilities of 5-10 percent for the northern Blue
Mountains.

Looking ahead, an Arctic air mass is possible (a solution
presented by roughly 60 percent of ensemble members) by the
weekend into early next week. Will lowland snow accompany this
cooler air mass? Confidence is still too low to discuss details,
so stay tuned for more details in the coming days.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  35  47  26  45 /  90  20   0  10
ALW  37  46  31  44 /  90  40  10  10
PSC  34  51  26  42 /  70  10   0  10
YKM  29  49  26  42 /  30   0   0  10
HRI  36  50  26  43 /  80  10   0  10
ELN  29  45  24  39 /  30   0   0  10
RDM  27  46  20  48 /  60  10   0  10
LGD  33  45  24  43 /  90  50  10  10
GCD  34  45  24  47 /  60  40   0  10
DLS  38  50  32  43 /  80  10   0  30

&&

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

$$

DISCUSSION...86
AVIATION...97