635
FXUS66 KPDT 222223
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
223 PM PST Wed Jan 22 2025

.SHORT TERM...Tonight through Friday...Little to talk about this
afternoon as water vapor imagery shows the PacNW under the
influence of high pressure aloft. This has led to mostly clear
skies today, though a thin layer of cirrus is entering central and
eastern WA at this time.

Tonight through late tomorrow morning, the PacNW will continue to
be under the influence of upper level ridging. This will result
in continued dry conditions area-wide, with morning temperatures
in the teens to lower 20s. While mostly clear conditions are
expected, areas of patchy fog may develop along the Columbia,
Snake, Walla Walla, and Yakima rivers (20-30% confidence in
extent/timing). The upper ridge will flatten tomorrow afternoon as
an upper trough dives towards the PacNW through BC with
increasing mid to upper level cloud cover. Well ahead of the
trough approach Thursday morning, surface pressure gradients will
tighten between the Columbia Basin and Lower Treasure valley,
resulting in breezy southerly winds developing in the Grande Ronde
valley and along the base of the Blue Mountain foothills.

Thursday night through Friday afternoon, the upper trough will
dive south across the PacNW, continuing to provide mid to upper
level cloud cover, while winds along the Blue mountain foothills
and the Grande Ronde valley will weaken. Due to the inland track
of the upper trough, this system will have very little moisture
available to bring any appreciable snow accumulations to the
mountains of the forecast area. In fact, the NBM is showing only
25-45% chances of just 0.1 inches of snow accumulations across our
mountain zones. Friday afternoon and night, a deep northerly flow
will develop as the upper trough continues to travel south of the
region. Cold air advection under this flow regime will allow a
modified arctic airmass to filter back into the PacNW with
widespread overnight low temperatures dipping into the single
digits to teens. Lawhorn/82


.LONG TERM...Saturday through Wednesday...

Key Points:

1. Dry and cool conditions persist.
2. Coldest temperatures on Saturday/Sunday.
3. Next system arrives late next week.

A ridge will sit just offshore of WA/OR through early next week,
funneling in dry and cool north/north-eastern flow aloft into the
PacNW. PoP chances will remain 0% for much of the CWA. Winds will be
breezy Saturday afternoon to Saturday evening across portions of the
Columbia Basin, with winds gusting 15-25 mph. Afterwards, winds will
calm down going into Sunday and remain light and variable. The
biggest story for the extended will be the cold temperatures as a
result of the northerly winds aloft. Temperatures will be at their
coldest on Saturday, with most areas in the CWA according to the NBM
having a 60-100% chance of the high temperature remaining below
freezing. Areas in higher elevations and the Foothills of the Blues
have 70-100% chances of low temps dipping below 20 degrees. Gradual
warming will occur through the extended, with highs across the area
rising to the mid to upper-40s across the CWA by the end of the
extended.

Models are in good agreement that this cool and dry pattern will
persist through mid-next week. Only 18% of guidance members suggest
a shortwave forming over the area, bringing in some precip chances
to the Cascades by Wednesday morning. Confidence is moderate (50-
60%) this far out that the system will not occur until right after
the long term, but it will requiring monitoring to see how the
timing of this system plays out as we head into the weekend. /95


&&

.AVIATION...00Z TAFs...Thin cirrus have been observed this
afternoon, but mid and high level clouds AOA 14K feet will spread
across the region this evening and continue through most of
Thursday. At DLS, web cams showed SCT stratus clouds early this
morning. An easterly gradient and low level upslope will cause the
stratus to become BKN early Thursday morning. Confidence was high
enough (70%) to include in the TAF. Otherwise, light winds will
continue for the next 24 hours. Wister/85

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  21  37  21  36 /   0   0  10  10
ALW  22  37  23  36 /   0   0  10  10
PSC  23  36  25  40 /   0   0  10  10
YKM  19  35  21  41 /   0   0   0  10
HRI  23  36  24  39 /   0   0  10  10
ELN  19  37  23  38 /   0   0   0   0
RDM  20  49  21  37 /   0   0   0   0
LGD  18  37  20  36 /   0   0  10  10
GCD  21  46  23  38 /   0   0   0  10
DLS  26  41  28  43 /   0   0   0  10

&&

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

$$

SHORT TERM...82
LONG TERM....95
AVIATION...85