West Side, Washington Weather Forecast Discussion

540
FXUS66 KPDT 161719
AFDPDT
Area Forecast Discussion
National Weather Service Pendleton OR
1019 AM PDT Tue Sep 16 2025
Updated Aviation Discussion
.AVIATION...An east to west directed surface pressure gradient was
in place across the region this morning while GOES satellite showed
dry air in the mid and low levels as clear sky prevailed region
wide. VFR conditions are anticipated through the TAF period as
prevailing winds remain light east to northeasterly with local
terrain effects, with the exception of DLS where occasional gusts
winds to around 20 knots can be expected through 00 UTC.
&&
PREV DISCUSSION... /issued 207 PM PDT Mon Sep 15 2025/
DISCUSSION...
Key Messages:
1. Warm and dry trend through midweek.
2. Warm temperatures persist through Saturday.
3. Next chance of showers over the weekend.
Current radar and visible satellite imagery shows dry conditions,
with a few high level clouds moving south along the northern Blue
Mountains. This is a result of an upper level ridge building
along the Washington/Oregon coasts coupled with a thermal trough
developing over the Umpqua and Willamette Valleys west of the
Cascades. The building thermal trough and upper level ridge have
allowed for east winds to develop across the area, which will
enhance this evening through Tuesday. The breeziest conditions
will occur through the Eastern Gorge and the Kittitas Valley with
sustained winds of 10-15 mph with gusts of between 20-25 mph
Tuesday afternoon. Confidence in these wind values is moderate
(50-70%) via the NBM. However, humidities in these areas hover
between 40-50%, well above critical fire weather values. A drier
and warmer airmass will move over the area to bump high
temperatures from the low to mid-70s today into the low to mid-80s
on Tuesday. Humidities will also trend downward into the mid-to
upper teens across Central Oregon and around 30% across South-
Central Washington by Tuesday. Overnight humidities will continue
to trend drier and become moderate to poor (35-50%) Wednesday
through Friday across higher terrain of the east slopes of the
Cascades, eastern mountains, and the John Day Highlands.
The upper level ridge strengthens Tuesday before shifting to our
east on Wednesday as an upper level trough approaches the coast.
This trough will slow and shear north, keeping conditions dry but
breezy as a pressure gradient develops between the approaching
trough and antecedent ridge. The approaching trough will also
promote southwest flow aloft to keep temperatures about 10 degrees
above normal as high temperatures stay in the mid-to upper 80s
across the Basin, Blue Mountain foothills, and the Yakima Valley
Wednesday through Friday. The NBM suggests a high confidence
(85-95% chance) of high temperatures reaching 85 or greater over
the aforementioned areas.
Ensemble members are in good agreement with an upper level low
pressure developing off the California coast on Friday, with 68%
of ensembles suggesting the low merge with a passing upper level
trough to provide light showers Saturday evening through Sunday.
Both features look rather weak as flow is more zonal across the
Pacific Northwest. These systems are also following a dry and hot
airmass associated with the departing ridge, so only a couple
hundredths of a inch of rainfall is anticipated across the east
slopes of the Cascades and the Blue Mountains, with all other
areas looking to stay dry at this time. 75
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT  80  52  85  55 /   0   0   0   0
ALW  82  58  87  59 /   0   0   0   0
PSC  82  50  86  52 /   0   0   0   0
YKM  81  54  87  55 /   0   0   0   0
HRI  82  52  86  53 /   0   0   0   0
ELN  80  49  85  51 /   0   0   0   0
RDM  82  44  84  45 /   0   0   0   0
LGD  81  47  85  49 /   0   0   0   0
GCD  82  47  86  49 /   0   0   0   0
DLS  85  57  88  58 /   0   0   0   0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&
$$
SHORT TERM...99
LONG TERM....99
AVIATION...71

NWS PDT Office Area Forecast Discussion