342
FXUS66 KPDT 081033
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
333 AM PDT Tue Sep 8 2026

.KEY MESSAGES...

- Warming and drying trend through midweek

- Breezy winds Thursday across the Gorge and Kittitas Valley

- Afternoon thunderstorms expected Saturday

&&

.DISCUSSION...
Current radar and infrared satellite imagery shows a light
shower over eastern Wallowa county with some high level clouds
moving in from the north as a system continues to depart to the
east. In its wake, a transient upper level ridge will move over
the region to promote clearing skies and warming temperatures.
Highs are expected to increase about 5 degrees from Monday,
reaching into the upper 70s to low 80s across the Columbia
Basin, Gorge, Central Oregon, and the Blue Mountain foothills.
This warming trend will persist on Wednesday as flow aloft turns
from the northwest to the west, allowing high temperatures to
bump up another 5 degrees - reaching near to slightly above
normal averages for this time of year. Afternoon humidities will
also be on the decline, dropping between 15-25% across Central
Oregon and portions of the Eastern Mountains on Wednesday.
Moderate overnight humidity recoveries will also be present
Wednesday night into Thursday morning, with values in the 40-50%
range across Central Oregon.

Near normal temperatures extend into Thursday as the transient
ridge exits east. This is ahead of the next system that is
dropping down the British Columbia coast, pushing inland north
of Vancouver Island early Thursday morning. The upper level
trough will infiltrate into the Pacific Northwest Thursday
afternoon as a high pressure strengthens over the Four Corners
region and shifts west. These two synoptic features will allow
for a tightened pressure gradient to develop across the area,
more specifically along the Cascades. As a result, breezy to
windy conditions are likely through the Columbia Gorge,
Kittitas Valley, and the Simcoe Highlands. Current guidance
suggests that winds are expected to peak between 1 PM and 7 PM.
Kittitas Valley should experience the highest winds on Thursday,
with the NBM suggesting a 22% chance of reaching Wind Advisory
criteria (45 mph or greater). This chance is expected to
increase as the event nears as the GFS and NAM both highlight a
9-10 mb difference between Pane Field (PAE) and Pasco (PSC). In
addition, there are only 20% of ensemble members that suggest a
stronger transient ridge which would relate to slightly lower
expected winds - with 68% of members highlighting slightly
higher winds over the aforementioned areas. Thus, A Wind
Advisory is probable (50-60%) over the Kittitas Valley Thursday
afternoon, with lower chances for the Simcoe Highlands (30-40%)
and the Columbia Gorge (25-35%).

Thursday`s system effectively flattens the building Four Corners
ridge and quickly ejects east, but a much stronger system
follows shortly behind. This system drops more inland from
Eastern Alaska and northwest British Columbia before shifting
offshore just north of Vancouver Island. The offshore motion
will allow it to strengthen and pull additional moisture from a
closed low, located over the Eastern Pacific, on its way into
the Oregon coast. It also provides enough time from the earlier
system for a weak area of high pressure to attempt to build.
These two factors will attribute to isolated afternoon
thunderstorm chances across the east slopes of the Cascades,
Central Oregon, and the Yakima/Kittitas Valleys on Saturday.
Guidance is struggling with the timing and strength of these
systems, but currently 56% of ensemble members showcase an
earlier and stronger dropping system, which would provide
widespread 150-300 J/kg CAPE values. These would also relate to
a wetter scenario, with 56% of members bringing widespread rain
amounts of 0.05-0.15". The remaining 44% of members keep rain
amounts either limited to the east slopes of the Cascades or
widespread rain amounts of 0.04" or less. Light, lingering
showers are expected across Wallowa county on Sunday as the
system slowly departs east into Monday. Both AI ECMWF and GFS
guidance hints at northwest flow aloft persisting through early
next week, with a weak, embedded system arriving Tuesday. 75



&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
VFR conditions currently at all sites, which will stay the
course through the period. FEW 15kft ceilings at KYKM, KALW,
KPSC, and FEW 25kft ceilings at KPDT today, becoming more broken
late in the evening. Winds to stay light and below 10kts for all
sites. 75

&&

.Preliminary Point Temps/PoPs...
PDT  76  46  82  52 /   0   0   0   0
ALW  77  52  83  59 /   0   0   0   0
PSC  80  49  85  53 /   0   0   0   0
YKM  79  52  84  55 /   0   0   0   0
HRI  80  47  85  52 /   0   0   0   0
ELN  77  48  81  53 /   0   0   0   0
RDM  75  40  85  44 /   0   0   0   0
LGD  74  44  83  48 /   0   0   0   0
GCD  76  44  86  49 /   0   0   0   0
DLS  81  55  86  57 /   0   0   0   0

&&

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

&&

$$

DISCUSSION...75
AVIATION...75