643
FXUS66 KPDT 261656
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
956 AM PDT Sat Sep 26 2026

.KEY MESSAGES...
- Dry conditions and light winds will prevail through Monday

- Light mountain rain showers and breezy winds return Tuesday,
  with growing uncertainty in shower chances Wednesday onward

- Near to below normal temperatures through the period

&&

.DISCUSSION...
Water vapor satellite imagery tonight shows
yesterday`s trough has lifted into Canada while the next trough
is beginning to develop offshore. As for nighttime satellite
imagery, stratus is seen hugging higher terrain of the Cascades,
Wallowas, and the Elkhorn crest while cirrus spreads from
southwest to northeast across the forecast area.

Today through Monday: Weak broad troughing developing offshore
the PacNW tonight will slowly migrate inland through this
weekend. Model guidance continues to depict the main energy and
jet-max of the the trough remaining well south of the PacNW,
resulting in a weak, split flow aloft. This pattern will result
in dry conditions, light winds, and below normal temperatures.
However, hires short-term and global deterministic model
guidance is hinting at a shortwave riding up the leeward side of
the trough Sunday, resulting in showers mainly across
southeastern OR. While chances at this time are less than 10%
across the mountainous terrain of Grant, Union, and Wallowa
counties, a slight delay in the trough passage could bring an
isolated shower or two to these areas.

Monday, the upper trough will continue to dig south of the area
with zonal flow developing over the PacNW. Dry conditions with
light winds will prevail Monday with near normal temperatures.

Tuesday through Friday: Ensemble cluster guidance is in good
agreement of a shortwave trough to the north and attendant
frontal boundary clipping the northern half of the forecast
area Tuesday. Showers will develop across the northern OR
Cascade crest and WA Cascades throughout Tuesday with light
showers developing latter half of Tuesday across the northern
Blues (confidence 55-65%). In the lower elevations, breezy
westerly winds will develop through the afternoon and evening,
with wind gusts peaking around 35 mph in portions of the
Columbia Basin.

Tuesday night through Wednesday, disagreement grows amongst
ensemble members in the timing of the shortwave trough exit,
with a little over 50% of members showing mountain showers
persisting into late Wednesday morning, and 40% of members
favoring only WA Cascade showers through Wednesday afternoon.
These two solutions also depict different synoptic evolutions:
the former solution favors ridging building over the PacNW while
the latter favors near zonal flow aloft and broad troughing
offshore.

Thursday, ensemble guidance remains in disagreement in the
timing/strength of an incoming low pressure feature. While 48%
of members favor ridging persisting into Thursday morning, they
disagree on the strength of a shortwave riding over the ridge
and subsequent extent/intensity in mountain precipitation.
Meanwhile, another 33% of members favor a shallow trough sliding
into the PacNW with mountain showers developing Thursday. By
Friday, 80% of members favor some form of ridging developing
aloft or just offshore the PacNW, while the remaining favor
troughing over the region.

Overall, confidence is low (15-25%) in the forecast Wednesday
through Friday next week in regards to precipitation chances,
but there is moderate confidence (45-60%) in near to below
normal temperatures. Lawhorn/82

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...

VFR conditions prevail throughout the region. Currently clouds
are moving out of the region bringing clear skies and dry
sinking air. Winds are light over all with KBDN/KRDM having an
increased chance around 0z. Wind are relativity variable with
mostly diurnal wind patterns.

&&

.Preliminary Point Temps/PoPs...
PDT  64  37  63  37 /   0   0   0   0
ALW  65  41  65  43 /   0   0   0   0
PSC  68  40  71  40 /   0   0   0   0
YKM  64  41  67  41 /   0   0   0   0
HRI  67  40  68  39 /   0   0   0   0
ELN  60  36  63  36 /   0   0   0   0
RDM  64  33  63  31 /   0   0   0   0
LGD  64  38  66  37 /   0   0   0   0
GCD  67  40  70  37 /   0   0   0   0
DLS  68  46  71  45 /   0   0   0   0

&&

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

&&

$$

DISCUSSION...82
AVIATION...18/82