316
FXUS66 KPDT 271151
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
451 AM PDT Fri Sep 27 2024


SHORT TERM...Today through Sunday Night...

Key Messages:

1. Breezy winds linger today across the east slopes.

2. Widespread breezy winds late Saturday through Sunday.

3. Drying conditions through the weekend, warmer through Saturday.

Current radar and infrared satellite imagery shows light returns
along the Washington Cascade crest with dry conditions and mostly
clear skies elsewhere across the region. This is in response to
a weak shortwave and associated cold front clipping northern
Washington. High pressure, centered over the Desert Southwest,
will continue to strengthen and infiltrate into the Interior
Northwest, leading to drying conditions over the Washington
Cascades through the morning as the shortwave also departs to our
northeast. The weak cold front associated with the exiting
shortwave will pass through from northwest to southeast and allow
a pressure gradient to develop over the Kittitas Valley. This
will keep winds elevated through the day today as sustained
northwest winds of 15-20 mph and gusts of up to 25 mph are
expected to peak during the late morning and early afternoon.

Transient ridging will occur late Friday into Saturday as winds
dissipate, skies stay mostly clear, and conditions stay dry.
However, another upper level shortwave will approach the
Washington coast Saturday afternoon to allow for increased cloud
cover overnight and breezy conditions to return across the
Kittitas Valley, Gorge, and portions of the Basin. The GFS, NAM,
and SREF all suggest a pressure gradient of 6-9 mb setting up
between Everett (KPAE) and Pasco (KPSC) after 5 PM Saturday and
extending into Sunday afternoon. These values relate to sustained
northwest winds of 25-30 mph and gusts of up to 40 mph over the
Kittitas Valley. Sustained west winds through the Gorge and
portions of the Blue Mountain foothills are expected to reach
between 20-25 mph with gusts of up to 35 mph. There is high
confidence (80-90%) in these elevated winds, as the NBM
advertises a 75-95% chance of sustained winds of 25 mph or greater
over the Kittitas Valley, a 65-85% chance through the Gorge, and
a 45-65% chance along the Blue Mountain foothills. The NBM also
suggest a 55-85% chance of gusts reaching 40 mph or greater across
the Kittitas Valley, a 35-55% chance through the Gorge, and a
20-40% chance along the Blue Mountain foothills. Chances stay low
(25%) in winds reaching advisory criteria as the NBM showcases a
20-30% chance of sustained winds of 30 mph or greater and gusts of
45 mph or greater over the Kittitas Valley and Gorge, dropping to
a 10% chance through the Blue Mountain foothills.

Zonal flow aloft from the west today will attribute to continued
warming and drying as high temperatures bump up 3 to 7 degrees
from Thursday as highs break into the low 80s across lower
elevations of the Basin. Temperatures will increase another 1 to 3
degrees on Saturday before a significant drop of 7 to 10 degrees
is expected on Sunday associated with the passing shortwave.
Conditions will continue to dry through the weekend with Sunday
afternoons humidities dropping into the low 20s to mid-teens across
Central Oregon and the John-Day Basin. These critical humidities are
not expected to coincide with the highest winds located over our
Gorge and eastern slopes of the Cascade zones, but enhanced fire
spread will be a concern as widespread breezy winds are anticipated.
75


LONG TERM...Monday through Friday...

Through Wednesday, the PacNW will enter a quiet weather pattern
as the upper builds over. Light winds will be less than 12 mph
Monday (>70% confidence).

Slight chance of showers (15-30%) could occur Tuesday through
Wednesday morning at the crest of WA Cascades due to the orographic
lifting from the cold front off British Columbia area. Models are in
good agreement with the arrival of the front. Breezy conditions will
develop up to 25 mph Tuesday into Wednesday morning at the Kittitas
and Yakima Valley, eastern CR Gorge and Simcoe Highlands (50-80%
probability). The PacNW will then enter another ridge Thursday with
light winds remaining throughout the day.

Friday, the upper trough moves inland of the PacNW with the
associated cold front. This could increase chances for precip due to
the orographic lifting, but chances are low (<30%). Friday afternoon
into evening, breezy winds will also return at 15-25 mph at the
Cascade Gaps including central OR (50-70% probability). Though,
models begin to differ where the GFS show the trough over the region
with the cold front sooner than ECWMF with Canadian favoring dry
conditions. Given the timing differences and uncertainties, showers
could happen depending on how this trough behaves (<30% confidence).
Feaster/97

AVIATION...12Z TAFS...VFR conditions prevail through the TAF
period. Mid to high (FEW-BKN at 120-250) clouds will continue for
the next 24 hours. Winds will be less then 12 kts for all sites.
Feaster/97

&&


.PRELIMINARY POINT TEMPS/POPS...
PDT  77  47  78  48 /   0   0   0   0
ALW  79  51  80  53 /   0   0   0   0
PSC  79  51  80  52 /   0   0   0   0
YKM  77  47  79  44 /   0   0   0   0
HRI  80  50  80  51 /   0   0   0   0
ELN  73  45  77  46 /   0   0   0  10
RDM  78  43  82  42 /   0   0   0   0
LGD  80  48  88  48 /   0   0   0   0
GCD  83  51  90  45 /   0   0   0   0
DLS  79  51  82  52 /   0   0   0   0

&&

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

$$

SHORT TERM...75
LONG TERM....97
AVIATION...97