502
FXUS66 KPDT 042249
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
249 PM PST Thu Dec 4 2025

.DISCUSSION...

Key Messages:

1. Showers and mountain snow persists through Friday afternoon.

2. Windy conditions Friday afternoon through Saturday morning.
   *Wind Advisories Issued*

3. Widespread rain returns Sunday, workweek river flood concerns.
   *Hydrologic Outlook Issued*


Current radar and visible satellite imagery showing light to
moderate showers across the Columbia Basin, foothills, Blue
Mountains, and the Cascades under overcast skies. This is in
response an upper level shortwave and associated frontal system
that will slowly pass through the Pacific Northwest over the next
24 to 36 hours. An additional 0.25-0.50" of rainfall is
anticipated this evening across the Columbia Basin, Blue Mountain
foothills, Wallowa county, and the John Day Basin, with less than
0.05" through Central Oregon, Eastern Gorge, and the
Yakima/Kittitas Valleys. Snow levels will hover between 4500-5500
feet through the remainder of the day, leading to an additional
2-6 inches of snowfall over the northern Blue Mountains, 1-2
inches for the Southern Blue Mountains, and less than an inch over
the Washington Cascades above 4000 feet. An incoming cold front
Friday will increase rain showers across the region through the
morning and early afternoon before becoming more confined along
the Cascade and Blue Mountains in the evening into Saturday
morning. Friday`s rain amounts are expected to reach 0.25-0.50"
along the east slopes of the Cascades, Grande Ronde Valley, and
Wallowa County, 0.10-0.20" along the Blue Mountain foothills and
the John Day Basin, and less than 0.10" through the Columbia
Basin, Central Oregon, and the Yakima/Kittitas Valleys. Snow
levels will be on the rise and into the 7500-8500 foot range
through Friday afternoon/evening, leading to only an additional 1
to 2 inches of snowfall over higher terrain across the Cascades
and northern Blue Mountains.

The primary concern in the short-term resides with windy
conditions associated with the passage of a stout cold front
Friday evening into Saturday morning. As a result, a 10-11.5 mb
pressure gradient will develop across the Lower Columbia Basin
(between PDX and GEG) as advertised by the GFS, NAM, and SREF.
These values relate to sustained west winds of 20-30 mph with
gusts of up to 55 mph possible. Confidence in these values is
moderate to high as the NBM and HREF highlight a 55-75% chance of
wind gusts reaching 45 mph or greater and a 40-70% chance of gusts
reaching 50 mph or greater. Thus, a Wind Advisory has been issued
from 4 PM Friday through 10 AM Saturday for the Eastern Columbia
River Gorge, Simcoe Highlands, Blue Mountain foothills of Oregon,
North-Central Oregon, and the Lower Columbia Basin of Oregon; and
from 7 PM Friday through 7 AM Saturday for the Kittitas Valley
and the Blue Mountain foothills of Washington. Peak winds are
expected to occur overnight between 1 AM and 4 AM Saturday, with
highest winds likely across the Simcoe Highlands.

Ensemble guidance is in agreement with a substantial Atmospheric
River (AR) event impacting the Pacific Northwest early to mid-
week, allowing for significant, persistent rainfall Monday
evening through Wednesday evening and increasing snow levels of
between 6000-8000 feet. Confidence in specific rain amounts is
lacking, but the current forecast calls for 2-4 inches across the
Cascades, 1-2 inches over the Blue Mountains, and 0.20-0.50" over
the Lower Columbia Basin, Central Oregon, John Day Basin, and the
Blue Mountain foothills during that 48 hour period. These wet and
warm conditions will lead to river flooding concerns, primarily
over the Naches and Yakima Rivers as both are forecast to reach
action stage either Tuesday or Wednesday. Even though ensemble
guidance is in agreement with the overall pattern of an incoming
AR event, the location and overall amount of moisture is still in
question as guidance struggles with how much the upper level ridge
located off the coast of California suppresses. The more it
suppresses and pushes further south, the more south and over the
area the AR moisture plume gets directed. 53% of ensemble members
suggest slightly more precipitation/moisture over the Washington
Cascades, which would provide additional confidence in the Yakima
and Naches Rivers reaching action stage. The Northwest River
Forecast Center is currently advertising a 31%-63% chance of the
Naches River reaching Action Stage and a 21%-28% chance of the
Yakima River reaching Action Stage. At this time, there is a 5-9%
chance of either river reaching minor flood stage. 75




&&

.AVIATION...00Z TAFs...The rain has helped a few TAF sites clear out
from the fog. Currently DLS/RDM/YKM are all VFR. PSC/YKM are fluxing
between VFR-MVFR due to CIGs sloshing around. PDT is LIFR due to a
dense fog bank has just rolled in, ALW is MVFR due to both low CIGs
and VSBY less than 5SM. This will be the case through much of the
period as the CIGs and VSBY will fluctuate. Winds will be of no
assistance in pushing the fog out either as may sites will remain
below 6kts except DLS who will be gusty and VFR through 04Z before
slowing.


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  38  55  41  51 /  80  90  40  40
ALW  38  51  42  51 /  90 100  60  50
PSC  36  54  41  55 /  60  80  10  10
YKM  32  51  38  55 /  40  70  40  20
HRI  38  55  42  55 /  70  90  20  20
ELN  34  46  35  48 /  50  80  60  40
RDM  37  54  33  51 /  50  90  30  10
LGD  35  48  38  46 / 100 100  80  70
GCD  37  49  36  46 / 100 100  50  40
DLS  43  57  47  55 /  70  90  80  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 4 PM Friday to 10 AM PST Saturday for ORZ041-
     044-507-508-510.

WA...Wind Advisory from 4 PM Friday to 10 AM PST Saturday for WAZ024-
     521.

     Wind Advisory from 7 PM Friday to 7 AM PST Saturday for WAZ026-
     029.

&&

$$

DISCUSSION...75
AVIATION...90