557
FXUS66 KPDT 242120
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
219 PM PDT Thu Sep 24 2026

.KEY MESSAGES...

- Widespread showers and breezy to windy conditions develop Friday
  morning into Friday night.
 ***Wind Advisory in effect from 8 AM Friday through 11 PM Friday***

- Dry and light wind conditions return this weekend with
  temperatures below normal.

- Mountain showers and at or below seasonal temperatures Monday
  onward

&&

.DISCUSSION...
Current satellite imagery shows high and mid-level clouds moving in
over the forecast area which might make temperatures cooler than the
forecasted high temperature for the day, while surface observations
are relatively calm and quiet.

Friday...As the upper-level trough and attendant low propagate
inland from the coastal PacNW, there is a chance (80-90%) of
widespread showers across much of Central and northeast Oregon
and into central southern WA early Friday morning. As this
system moves through the area, model guidance and ensembles show
rain showers beginning after midnight near the Cascades with
more widespread rain beginning after 8 AM PDT. There will be a
(70-90%) chance for measurable rain for most of the forecasted
area Friday, with a chance (80-90%) for wetting rain, more so in
the mountainous areas near the Cascades, Ochoco Mountains, and
Southern/Northern Blues. At least 0.05-0.2 inches are forecasted
elsewhere in the forecast area (50-60%). Along with this
precipitation, the upper trough and surface low system will
bring gusty west-southwesterly winds to much of the forecast
area (85-90%). Winds will be 25-30 mph with gusts up to 35-45
mph across the Cascade Gaps and Columbia Basin due to the strong
low-level jet moving through and mixing down to the surface, as
well as the Rattlesnake Ridge and Horse Heaven Hills (85-90%).
Winds will be 15-25 mph with gusts up to 35 mph elsewhere
(70-80%). Yakima and Kittitas Valleys could see gusts 45 mph or
higher but chances are lower (35-40%) Friday afternoon.

Saturday-Sunday...Showers and windy conditions should diminish late
Friday night into Saturday morning as the upper trough and low
propagate northeast out of the forecast area. Relatively dry
conditions are expected with the upper flow becoming more westerly
bringing light winds back into the area Saturday morning. Model
guidance shows a weak broad trough begin to develop offshore the
PacNW Saturday night, then slide into the region through Sunday, but
due to lack of moisture and strong upper-level flow, it will mostly
be dry with light wind conditions and temperatures in the low-mid
60s. Ames/01

Monday through Wednesday: Models show the region to be under a weak
split flow pattern with a ridge to the north of the region and a
trough to the southwest. This will bring continued dry conditions
and light winds through Monday night. In house calculations show the
temperatures to be nearly 5 degrees below seasonal average Monday
with temperatures in the mid to upper 60s with isolated locations in
the Basin seeing low 70s.

By Tuesday models are in agreement that the synoptic system will
shift more towards zonal flow. Clusters are in good agreement with
mainly the strength of the incoming system with mainly timing being
the lack of confidence. By Tuesday morning, light mountain showers
will begin over the Washington Cascades before shifting to the
crests of the Blue Mountains with 40% of the ensembles showing
precipitation chances. Temperatures will be slightly warmer than
Monday but still at or near normal seasonal temperatures in the low
70s (40-60%).

Wednesday models begin to phase apart with GFS showing northwest
flow aloft precipitation along the Cascade crests and a front coming
across the area while the Euro shows continued zonal flow with
precipitation along the WA Cascade crests. NBM appears to be a bit
more in line with the Euro with only showers along the WA Cascade
crests. In house calculations show temperatures to be at or near
seasonal normal with a few isolated locations seeing slightly above
normal temperatures. Temperatures are set to be in the low to mid
70s (50-60%). 90

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
KDLS/KRDM/KBDN:VFR should prevail for most of the forecast
period. Rain chances increase around 08Z Friday, ceiling are
expected to lower along side this to around 11,000ft.

KYKM/KPSC: VFR conditions prevail through the most of the
period. Rain chances increases after 07Z Friday, with the rain
ceilings are expected to lower to around 10,000ft.

KALW/KPDT: VFR conditions prevail though most of the forecast
period. Rain chances increases after 11Z Friday, ceilings
associated with this rain are expected to lower to about
8,000ft.

Toward the end of the forecast period a wind advisory comes
into effect for KYKM/KDLS/KPDT. Sustained winds for this
advisory are expected to prevail from the SW at 17-26 kts with
gusts up to 39-47 kts.

&&

.Preliminary Point Temps/PoPs...
PDT  50  70  41  64 /   0  80   0   0
ALW  55  70  46  66 /   0  90  10   0
PSC  52  73  42  68 /  10  80   0   0
YKM  54  66  40  64 /  60  40   0   0
HRI  52  72  42  67 /  10  80   0   0
ELN  49  61  36  59 /  70  60  10   0
RDM  44  60  31  63 /  60  20   0   0
LGD  52  67  39  65 /   0  50  10   0
GCD  53  67  38  67 /   0  50   0   0
DLS  56  67  45  68 /  70  60  10   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory from 8 AM to 11 PM PDT Friday for WAZ024-027-521.
OR...Wind Advisory from 8 AM to 11 PM PDT Friday for ORZ041-044-507-
     508-510.

&&

$$

DISCUSSION...01/90
AVIATION...18