515
FXUS66 KPDT 051753
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1053 AM PDT Sat Sep 5 2026

.KEY MESSAGES...
- Periodic showers will continue to impact the region this
  weekend, with best chances across the mountains

- Low chances (15-25%) of isolated thunderstorms mainly across
  mountainous terrain through Monday

- Mostly dry conditions with light winds and seasonable
  temperatures the remainder of next week

&&

.DISCUSSION...
Water vapor satellite imagery tonight shows an
upper level low over the PacNW, with a shortwave impulse
swinging north around the low and across the forecast area.
Nighttime satellite imagery shows partly to mostly cloudy
conditions across the forecast area with a few areas of
stratus/fog evident in portions of central OR.

The aforementioned shortwave impulse will continue to lift north
across the forecast area into the morning hours, with radar
showing a ling of isolated showers across portions of the
Columbia Basin and a few isolated showers/thunderstorms across
the eastern mountains as well.

The PacNW will continue to be under the influence of the upper
closed low through Monday, with persistent rain chances
(rain/snow mix above 8kft) over the mountain zones. Afternoon
temperatures across the region will be nearly 10-15 degrees
below average each day, with afternoon high temperatures in the
mid 60s to mid 70s today and tomorrow (confidence 85-95%).
While the upper closed low will remain parked over the PacNW
through Sunday, the center of the low will remain west of the
Cascade crest through Sunday afternoon before pivoting northeast
and out of the region Sunday night through Monday afternoon.
(confidence 70-85%). Today, rain shower chances will be tied to
the shortwave impulse passage this morning, followed by another
shortwave passage this afternoon and evening. CAMs indicate that
the best chances this afternoon will be along the WA Cascade
crest and the northern Blues for more organized shower activity,
with a few isolated showers elsewhere. Sunday, shower activity
will become more widespread as the upper low swings east and
north, with the best chances in the lower elevations Sunday
afternoon and evening. Isolated thunderstorms will be possible
over the mountains today as weak instability develops with
additional support from the cold core of the low aloft. As for
precipitation amounts, the Cascades and Blues will see 0.1 to
0.25 inches of daily precip (confidence 70-90%), with locally
higher amounts where thunderstorms develop. Monday, the upper
level low passing over the Cascades will lead to a tightening
of the cross-Cascade surface pressure gradient, resulting in
breezy to locally gusty winds (15-30mph with gusts 30-45mph)
through the Cascade gaps and portions of the Columbia Basin. By
Monday evening, what is left of the upper level low will have
pushed east of the region, with showers diminishing area wide.

Tuesday, ensemble members are in good agreement of weak upper
troughing developing from the PacNW into the eastern Pacific, though
the forecast area will be within an area of split flow
(confidence 65-70%). Winds will remain light under this
pattern, with a warming trend bringing temperatures closer to
normal. By Wednesday, ensemble members depict a weak cut-off low
developing with remnants of TS Marie merging into the low well
west of the central CA coast while near zonal flow develops over
the PacNW later in the evening. This continues to result in dry
conditions across the region with near seasonable temperatures
and light winds (confidence 50-60%)

Thursday through Friday, disagreement grows amongst ensemble
members in the evolution of the synoptic pattern. While there is
great agreement in an upper trough diving south along the BC
coastline Thursday, ensemble members come into disagreement into
whether the cut-off low in the eastern Pacific merges into the
upper trough or not. Around three-quarters of the members agree
that the cut-off low will get swallowed into the flow with the
remaining energy lifting across the PacNW with showers, however
disagree on timing (~55% late Thursday, remaining 15-20%
sometime Friday). Regarding these solutions, there is low
confidence (25-30%) in precipitation details owing to the
uncertainty of remaining moisture from TS Marie. Otherwise, the
remaining members favor the low remaining in the eastern
Pacific, with mostly dry conditions across the forecast area
during this period. Lawhorn/82

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Showers continue to prevail through the forecast area through
tomorrow with on and off chances through the period. Will see
greater chances of precip along the central Oregon sites in the
later afternoon to evening hours tonight. Currently don`t have
MVFR or lower as confidence is lower in this set-up. There`s a 5
to 15 percent chance we can see moderate showers moving over
some of the TAF sites, reducing visibility and/or cloud decks
down to at least MVFR levels.

&&

.Preliminary Point Temps/PoPs...
PDT  70  45  68  48 /  30  10  30  40
ALW  72  50  71  52 /  30  10  10  60
PSC  75  48  73  50 /  20   0  20  30
YKM  72  51  72  52 /  40  10  30  10
HRI  73  49  71  50 /  20  10  30  30
ELN  69  45  71  48 /  50  10  20  20
RDM  67  40  61  37 /  20  60  90  50
LGD  72  43  72  46 /  30  10  50  80
GCD  70  45  69  46 /  40  10  70  80
DLS  74  55  71  55 /  30  30  50  10

&&

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

&&

$$

DISCUSSION...82
AVIATION...99