556
FXUS66 KPDT 072239
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
239 PM PST Sun Dec 7 2025

.DISCUSSION...Rest of Today: Light rain in the lower elevations
has tapered off this afternoon as rain/high elevation snow showers
have started to develop along the Cascade crest and portions of
the northern Blues. Showers will continue tonight as a quick
moving cold front and shortwave slides across the PacNW. Breezy
southwest winds will continue overnight behind the cold front
passage, but confidence is low (<20%) in wind gusts 45mph or
higher developing.

Monday through Thursday: Ensemble and deterministic guidance is in
good agreement that multiple surface frontal and upper shortwaves
will slide down the west side of an upper ridge of high pressure
in the northeast Pacific through the midweek, with each of these
systems sliding across the PacNW each day. These systems will also
be accompanied by a persistent plume of tropical to subtropical
moisture that will see IVT values of 500 to 750 kg/m/s, resulting
in high confidence of heavy rain developing across most mountain
zones through this period, while a cold front passage Monday night
into Tuesday will result in the best chance of moderate to locally
heavy rain in the lower elevations (confidence 70-85%). Due to
the warmer nature of the incoming AR, snow levels will mainly be
above 5.5kft throughout the AR duration, however a cold front
passage Monday night into Tuesday will briefly bring snow levels
down to pass level in the central WA Cascades with wet snow
developing in White, Snoqualmie, and Blewett passes. Otherwise, a
low level jet (50-70kts) will move over the PacNW by Monday
afternoon, with strong winds mixing down into Columbia Basin/Gorge
and adjacent valleys/foothills through Tuesday morning as the
cold front moves across the forecast area. Confidence is
moderate- high(70-85%) that sustained winds of 25-35mph with gusts
45-55mph will impact wind prone areas, with stronger gusts across
exposed ridges in the Columbia Plateau and along the Cascade
crest and east slopes.

Over a 3 day period ending Thursday morning (covering the peak of
the AR), the NBM shows the WA Cascade crest at a 50-70% chance for
at least 7 inches of QPF, while the Cascade crest overall will
see a 50-85% chance of receiving 5 inches or more of QPF, and the
northern Blue Mountains will see a 35-50% chance of at least 3
inches in the same period. Area rivers and streams will rise
beginning early this week as most of the incoming precipitation in
the mountains is expected to fall as rain (confidence 65-85%). Of
note, rivers originating from the WA Cascade east slopes will see
rises into at least action stage Monday night into Tuesday
morning (confidence 60-80%), with low confidence (10-25%) in
rivers reaching minor flood stages at this time.

By late Thursday, there remains good agreement that the upper
ridge offshore will amplify and nudge closer to the PacNW,
effectively moving the AR north of the region. Precip chances and
amounts will gradually wane from south to north throughout the
day, with dry conditions returning to the lower elevations by
Thursday night (confidence 55-75%).

Friday into the Weekend: Good agreement remains amongst ensemble
guidance that the upper ridge will remain amplified as the ridge
axis approaches the PacNW Friday and moves inland Saturday. This
will result in precipitation chances mainly across the WA Cascade
crest through this period, with dry conditions elsewhere. That
said, about 12% of ensemble cluster members (ECMWF, GFS, and
Canadian) do favor the ridge being less amplified as it moves
inland Saturday, resulting in light rain and high mountain snow
across the Cascade crest into Oregon and across the Blue
Mountains. Lawhorn/82


&&

.AVIATION...00Z TAFS...VFR conditions currently across all sites,
but conditions are expected to degrade to MVFR for KDLS toward the
end of the period due to reduced visibilities of 4SM and ceilings of
1kft. Light rain will be impacting all sites Monday morning, with
breezy winds anticipated for KPDT/KRDM/KBDN/KALW. Gusts at these
sites are likely to hover around 25 kts late Monday morning as a
cold front passes the area. 75


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  42  59  47  56 /  40  70  70  90
ALW  45  57  48  54 /  50  90  80  90
PSC  43  60  48  56 /  10  60  50  70
YKM  36  55  40  51 /  10  80  70  70
HRI  42  62  49  57 /  20  60  60  90
ELN  33  49  37  46 /  20  90  80  60
RDM  36  57  44  57 /  30  40  40  80
LGD  37  49  44  51 /  70  80  90 100
GCD  37  52  45  51 /  40  50  50  90
DLS  46  59  50  55 /  60  90  90  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 1 PM Monday to 7 AM PST Tuesday for ORZ041-
     510.

     Wind Advisory from 4 PM Monday to 7 AM PST Tuesday for ORZ044-
     507-508.

WA...Wind Advisory from 1 PM Monday to 7 AM PST Tuesday for WAZ024-
     521.

     Wind Advisory from 7 PM Monday to 7 AM PST Tuesday for
     WAZ027>029.

&&

$$

DISCUSSION...82
AVIATION...75