Pendleton, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

521
FXUS66 KPDT 291723
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
925 AM PST Wed Jan 29 2025

Updated Aviation Discussion

.AVIATION...18Z TAFs...A brief period of dense fog developed over
PSC earlier this morning, but the latest obs are showing signs of
improving with 1SM in visibility (CIGS 300 feet). Fog satellite
shows low stratus along the Columbia Rivre from PSC southward. The
rest of the terminal airports are clear with some fog west of ALW.
Tonight, high cirrus clouds will spread across the region.
Otherwise, light winds will continue for the next 24 hours. Wister/85

&&

.PREV DISCUSSION... /issued 207 AM PST Wed Jan 29 2025/

SHORT TERM...Today through Friday...Satellite imagery tonight
shows very little going on across the region, though there are
indications of patchy fog attempting to develop along the Columbia
River. The quiet and cold conditions across the region will
continue through Thursday as an upper level ridge centered
offshore gradually makes its way into the PacNW. Stable conditions
and low level inversions underneath the ridge will also lead to
air stagnation concerns persisting through Thursday night.

Thursday night through Friday, the quiet conditions across the
forecast area will give way to a period of active weather across
the PacNW. A warm front will move across the PacNW and bring
increasing precipitation chances across much of the forecast area
by Friday morning, followed by a shortwave trough passage through
Friday night. Warm air advection with the frontal passage will
result in snow levels rising to around 4kft to 5kft, with the
heaviest snowfall occurring above pass level across our mountain
zones. At pass level in the Cascades, however, there is a 50-70%
chance of 4 inches or more of snow accumulations and a 70-85%
chance in the interior northern Blues through Friday night. Across
central and north central, the eastern Columbia River Gorge, and
portions of the northern Blue mountain foothills, chances of 0.25
inches of rain are 50-70%, while in western portions of the
Kittitas/Yakima valleys these chances are 30-60%. For the
remainder of the lower elevations, chances for at least 0.1 inches
of rain will 60-80%.

Lastly, ahead of the warm front passage, the pressure gradient
between the Columbia Basin and Baker valley will tighten and
locally breezy southerly winds will develop across the forecast
area. The strongest wind gusts will develop in the southern Grande
Ronde valley between 45-50mph. Winds will continue to gradually
strengthen through Friday with the frontal/shortwave passage
across the forecast area, with strongest winds through the Grande
Ronde valley, ridges in the Columbia Basin, and along the Blue
mountain foothills. Lawhorn/82

LONG TERM...Saturday through Wednesday...The picture for this
weekend`s wet forecast is slowly starting to become clearer as
models better align on how the upper-level pattern will evolve. That
being said, there are still some complications in the forecast that
could still effect many variables, including the magnitude of
precip and snow levels.

The main feature we`re monitoring over the weekend is an atmospheric
river that most models depict as aligning right over the forecast
area, bisecting Oregon and Washington. This feature will lead to a
sharp gradient in snow levels, as the zonal orientation of the upper-
level winds will help boost snow levels downstream of the Cascades,
with warmer air lying to the south of the atmospheric river axis and
colder air to the north. The biggest challenge with regards to the
forecast is how exactly the orientation of this axis evolves over
the course of the weekend. Most models seem to suggest that the axis
will develop a more SW orientation late Saturday into Sunday, which,
depending on how this shapes up, could lead to warmer snow levels
across the forecast area or an intrusion of cold air, primarily into
Washington, that would allow for more snowfall for the mountain
passes and even down into the lowlands of the Yakima and Kittitas
Valley. The GFS seems to lean toward the latter solution, with the
deterministic ECMWF depicting the former. Ensemble clustering does
overall suggest a consensus on a more SW tilt of the moisture
transport axis, but how far south cold air creeps into the forecast
area remains uncertain, as it should be noted that even a slight
deviation of this axis north and south could have big implications
on the snowfall forecast.

Overall, based on latest guidance, will say that confidence in
measurable snowfall occurring across the lowlands is going down (25-
35% chance of an inch or more occurring) as models tend to favor a
warmer solution. The biggest areas of concern would then be the
mountain passes, which are still expected to receive accumulating
snowfall, but uncertainty remains around amounts. The Cascade Passes
look to be on more of the receiving end of snow than the eastern
mountains, so confidence as of now is 70-80% over 6 inches through
the weekend for the Cascades, but only 10-20% for Meacham/I-84
through the Blues.

Otherwise, expect gusty downslope winds across the Basin on Saturday
with amplified zonal flow overhead, with a 45-55% chance of gusts
exceeding 40 mph across most of the Basin, followed by a return to
cold conditions as models depict troughing overhead heading into
next work week. We could still see some light snowfall from this
troughing, even in the lowlands with temperatures expected to drop,
but moisture will be nowhere near as robust as the atmospheric river
expected over the weekend. NBM probability currently suggests only
about a 30-40% chance of lowland snow over an inch Monday into
Tuesday, with the mountains seeing only around a 30% chance of snow
over 3 inches for the same timeframe. Evans/74

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  38  21  44  32 /   0   0   0  20
ALW  39  23  43  34 /   0   0   0  20
PSC  39  20  40  33 /   0   0   0  20
YKM  38  16  38  28 /   0   0   0  30
HRI  39  21  42  34 /   0   0   0  20
ELN  37  18  37  28 /   0   0   0  30
RDM  49  19  52  35 /   0   0   0  20
LGD  39  21  43  32 /   0   0   0  10
GCD  45  22  51  33 /   0   0   0  20
DLS  44  26  47  36 /   0   0   0  70

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 4 AM PST Friday for ORZ041-044-507-
     508-510-511.

WA...Air Stagnation Advisory until 4 AM PST Friday for WAZ024-026>029-
     521.

&&

$$

SHORT TERM...82
LONG TERM....82
AVIATION...74