648
FXUS66 KPDT 292231
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
331 PM PDT Sat Aug 29 2026

.KEY MESSAGES...
- Shower chances across the WA Cascades with low chance (5-15%)
  of isolated thunderstorms across the WA Cascade east slopes
  and northern Blues through this afternoon

- Elevated fire weather conditions will continue through this
  evening due to breezy winds

- Drying and warming trend Sunday through early Tuesday before
  an upper low passage late Tuesday into Friday brings
  increasing shower chances, breezy westerly winds, and cooler
  conditions

&&

.DISCUSSION...
Water vapor satellite imagery this afternoon shows
an upper level low sliding across northern WA, with visible
satellite and radar imagery showing isolated to scattered
showers/thunderstorms mainly in the Upper Columbia Basin. Breezy
winds have developed through the Cascade gaps and into the lower
elevations as well, with strongest winds being reported through
the Kittitas valley and along WA Cascade east slopes.

Rest of Today through Early Tuesday: Showers and any remaining
convection across the forecast area will diminish before this
evening as the upper low lifts northeast into Canada. The breezy
westerly winds that developed with the low passage will continue
into this evening as cold air advection behind the low will
maintain tightened surface pressure gradients. While RHs will
remain above critical criteria over the region, the breezy
winds will continue to present elevated fire weather conditions
across the lower elevations and along the Cascade east slopes.

The aforementioned cold air advection into the region will keep
temperatures about 3 to 8 degrees below normal through Sunday
afternoon, with some mountain valleys in the eastern mountains
looking at near to below freezing temperatures tonight
(confidence 65-80%). With winds expected to weaken and skies
remaining mostly clear, confidence is high enough (65-80%) to
warrant a freeze warning for tonight in the Wallowa valley.

Sunday through early Tuesday, upper level ridging will move over
the region, resulting in a warming and drying trend through this
period. At this time, given the increased high pressure over
the region and expected warming, confidence is low (25-35%) in
another round of near to below freezing temperatures developing
across most of our mountain valley locations.

Tuesday through Friday: Confidence is mod-high (60-80%) that an
active period of weather will develop through the remainder of
the work week. Ensemble cluster and deterministic guidance are
in agreement of a weakening upper low offshore becoming an open
wave and lifting northeast. The upper shortwave trough passage
over the PacNW will bring scattered shower chances across
mountain areas as well as in central OR with slight chance
(15-205% of isolated thunderstorms in central OR, WA Cascades,
and portions of the eastern mountains. Breezy westerly winds
will develop across the Lower Columbia Basin, central OR, and
portions of the eastern mountains Tuesday afternoon. RHs along
the periphery of the southern Blues will remain low into Tuesday
afternoon, resulting in elevated fire weather conditions as the
winds begin to increase.

Early Wednesday, ensemble cluster guidance is in good agreement
that an upper low will drop down the BC coastline and setup
just offshore the PacNW, increasing shower chances along the
Cascade crest. Late Wednesday into Friday, however, ensemble
cluster solutions are split between two solutions. The first
solution being the upper low sitting offshore through Thursday
into early Friday, then moving inland. The second solution is
for the upper low to push inland on Thursday and slowly move
across the region through Friday. The first solution would
result in rain shower chances developing across the eastern
mountains late Thursday into Friday; the second solution would
result in shower chances as early as Wednesday night, with
widespread mountain chances and isolated lower elevation chances
through Friday. Current confidence is moderate (50-60%) in
shower chances developing area-wide sometime late in the
workweek, but confidence is low (20-30%) in timing and
precipitation amounts. Lawhorn/82

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
VFR conditions continue with mid to high clouds around the
general area. Not expecting low ceilings, but could see some
overnight smoke makes it way down to the surface, temporarily
bringing MVFR conditions (5 to 15 percent chance for all TAF
sites). Otherwise, general breezy conditions across all sites,
with winds weakening as we head into the evening and overnight
hours.

&&

.Preliminary Point Temps/PoPs...
PDT  43  77  44  86 /   0   0   0   0
ALW  49  77  50  89 /   0   0   0   0
PSC  47  80  48  88 /   0   0   0   0
YKM  49  81  53  86 /   0   0   0   0
HRI  48  81  48  88 /   0   0   0   0
ELN  43  76  46  81 /   0   0   0   0
RDM  35  79  40  87 /   0   0   0   0
LGD  40  79  43  89 /   0   0   0   0
GCD  41  80  46  92 /   0   0   0   0
DLS  52  81  55  88 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...None.
OR...Air Quality Alert until noon PDT Monday for ORZ041-505-506-
     509>511.
     Freeze Warning from 1 AM to 9 AM PDT Sunday for ORZ050.

&&

$$

DISCUSSION...82
AVIATION...95