Ahtanum, Washington Weather Forecast Discussion

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FXUS66 KPDT 212338
AFDPDT
Area Forecast Discussion
National Weather Service Pendleton OR
438 PM PDT Sun Sep 21 2025
.UPDATED AVIATION.
.AVIATION...00Z TAFs...The front embedded with showers has mostly
moved out of the area and is mostly in the Eastern Mountain
region. Sites are cleared of the weather system, but a stray left
over shower is possible as the front continues to push to the
east. Didn`t put anything in the TAFs regarding precipitation
since confidence is very low that a passing shower will prevail.
For now, got sites clearing out as we go through the night and
overnight. Winds will lighten up as well going into the night
hours.
VFR conditions are expected to continue through the period, but
some guidance suggest the possibility of some overnight fog/mist
in the BDN/RDM area. Though chances are low (5-15%) for fog or
mist impeding visibilities overnight, we`ll keep an eye to see how
the rest of the night progresses if MVFR/IFR conditions will need
to be added. For now, not expecting any other VIS or CIG impacts
through the period.
&&
.PREV DISCUSSION... /issued 154 PM PDT Sun Sep 21 2025/
DISCUSSION...Current satellite imagery reveals a few features of
interest. An upper-level shortwave trough is tracking over Oregon
and Washington, and its attendant surface cold frontal boundary
is moving eastward across the Blue Mountain foothills. The front
will exit to the east later this evening leaving dry weather in
its wake as an upper-level ridge of high pressure builds overhead.
Farther south, a closed low is visible off the coast of southern
California. Analysis of ensemble clusters suggests the latter
feature will meander across the Southwest and Great Basin through
the week, likely (>80% chance) staying south of the OR/CA border
and having little impact on our weather.
Today, outside of the ongoing frontal rain band, there is a very
low chance (5-15%) of isolated thunderstorms across the Blue
Mountains, Blue Mountain foothills, and eastern half of the
Columbia Basin.
Cross-Cascade pressure gradients and isentropic descent behind
the cold front will drive breezy to windy westerly winds through
the Cascade gaps into wind-prone areas of the Columbia Basin
today. The Kittitas Valley has approached or exceeded Wind
Advisory thresholds, but have opted to hold off issuing any
highlights since it is localized to KELN.
A cool, dry air mass will be in place tonight through Monday night in
the wake of the cold front as an upper-level ridge of high
pressure builds overhead. There is some potential to see near- to
below-freezing temperatures tonight, most likely 31-36 degrees in
freeze-prone portions of central and northeast Oregon including
the Bend metro, the Grande Ronde Valley, and Wallowa Valley. Have
opted not to issue any Freeze Warnings/Watches due to low (80% chance) Tuesday through
Friday, though ensemble solutions diverge significantly by Friday
and Saturday. The main concern will be low afternoon relative
humidity and poor to moderate overnight recovery, especially
Tuesday night and Wednesday night. Little to no overlap of wind/rh
thresholds for Red Flag conditions are anticipated (80%
confidence).
Will note there is medium-high (60-70%) confidence in a return of
breezy to windy westerly winds Thursday through the Cascade gaps
and into the Columbia Basin. However, confidence in details of the
wind forecast is still low (

NWS PDT Office Area Forecast Discussion