363
FXUS66 KPDT 220533
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1033 PM PDT Wed Oct 21 2026

.Updated Aviation Discussion.


.KEY MESSAGES...
- Above-normal temperatures and dry conditions through tonight

- Return of showers and isolated thunderstorms to the eastern
  mountains tomorrow

- Breezy to gusty winds developing across the area Thursday
  night into Friday morning, with strongest winds through the
  Cascade gaps

- Moderate-high confidence (65-80%) in freezing morning
  temperatures across lower elevation area Saturday

&&

.DISCUSSION...
Water vapor satellite imagery this afternoon shows an upper
closed low off the coast of central CA, while a cold front
boundary approaches Vancouver Island to the north. As for over
the PacNW, little to talk about except for some partly cloudy
conditions with a cumulus field developing over the Wallowas and
Elkhorn Crest.

Today: While an upper low continues to sit off the central CA
coast today, the forecast area will sit under a weak south to
southwest flow aloft. Dry and seasonably warm conditions will
continue to impact the area today. To the south, the upper low
will begin to swing inland tonight, with precipitation ahead of
the low reaching southern OR late this evening and overnight.

Tomorrow and Friday: The PacNW will see a brief return to
unsettled weather as two separate systems arrive to the region.
These two systems will come in the form of an upper closed low
passing to the south and east and an upper trough with
attendant cold front sliding across the PacNW.

The upper closed low passage will be the main precipitation
maker through this period. Showers will begin to develop across
the high terrain south and east of John Day late tonight, then
spread to the remainder of the eastern mountains, central OR,
and the eastern half of the Columbia Basin by tomorrow
afternoon. Shower chances will dissipate from west to east
tomorrow evening through Friday morning as the upper low
continues east of the region. Between 5AM tomorrow and 5AM
Friday, there will be a 70-95% chance of 0.25 inches of rain
across the northern Blue Mountains, Elkhorn Crest, and Wallowa
County; along the Blue Mountain foothills and the remainder of
the eastern mountains, chances of 0.1 inches have come up
50-80%. In the remainder of the areas, there is a 30-60% chance
of at least 0.01 inches.

The upper trough and cold front passage tomorrow night through
Friday will bring wind impacts throughout the forecast area.
Winds will begin to increase through the Cascade gaps tomorrow
afternoon, and continue to strengthen overnight as the cold
front drags across the intermountain PacNW. Winds are currently
expected (confidence 70-85%) to peak overnight tomorrow into
early Friday morning between 25-35 mph with gusts to around 45
mph through the eastern Gorge and Kittitas Valley, while winds
will be slightly weaker (20-30mph with gusts up to 40 mph) in
portions of the Columbia Basin, Central OR, Cascade east slopes,
and eastern mountains (including Grande Ronde Valley). Breezy
winds will carry on into the afternoon Friday, but become light
by the nighttime hours.

Lastly, south to southwest flow aloft ahead of the low as well
as the low becoming a negative tilt trough over the Great Basin
will lead to increased instability over the eastern mountains.
SBCAPE will increase to between 200-250 J/kg across the
eastern mountains, leading to chances (15-25%) of isolated
thunderstorms developing tomorrow afternoon.

Saturday through Tuesday: After Friday, ensemble members are
still in some disagreement in the evolution of the synoptic
pattern. About 60% of members from the ECMWF, GFS, and Canadian
suites are in agreement of an upper low dropping down the BC
coastline by Saturday afternoon, then slowly passing through the
PacNW through early next week. That said, there is plenty of
disagreement amongst these members in regards to timing,
strength, and location of the low/upper trough moving over the
region. For now, confidence is at least moderate (55-60%) in
light mountain precipitation over the forecast area, but low
confidence (15-20%) in timing and accumulation amounts through
early next week.

Otherwise, there is good agreement that the earlier trough/cold
front passage will allow for a colder/drier airmass to settle
into the area Friday night through Saturday morning. The dry
conditions and potentially clear skies will at least help with
lowering temperatures to or below freezing in lower elevation
locations Saturday morning (confidence 65-80%). Will continue
to monitor for need of freeze watches/warnings. Lawhorn/82

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
VFR conditions currently across all sites, which will stay the
course through the period. An approaching system from the south
will bring light rain across most terminals in the afternoon,
with showers over KRDM/KBDN arriving mid-to-late morning. Winds
will increase slightly toward the end of the period for
KDLS/KRDM/KBDN.  75

&&

.Preliminary Point Temps/PoPs...
PDT  39  57  36  58 /   0  80  50   0
ALW  44  59  41  58 /   0  80  70   0
PSC  38  63  37  66 /   0  50  20   0
YKM  41  68  39  66 /   0   0   0   0
HRI  38  59  38  63 /   0  60  30   0
ELN  38  66  34  59 /   0   0   0   0
RDM  36  58  24  54 /   0  50  10   0
LGD  46  66  37  53 /   0  80  90  10
GCD  45  63  36  54 /  10  90  80  10
DLS  43  70  43  64 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory from 7 PM Thursday to 11 AM PDT Friday for
     WAZ024-026.
OR...Wind Advisory from 7 PM Thursday to 11 AM PDT Friday for
     ORZ041.

&&

$$

DISCUSSION...82
AVIATION...75