165
FXUS66 KPDT 041016
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
316 AM PDT Fri Sep 4 2026

.KEY MESSAGES...

- Periodic shower chances (35-75%) across the mountain zones
  will continue through early next week, with lower chances
  elsewhere

- Slight chance (15-25%) of isolated afternoon thunderstorms
  over the mountains through Monday

- Below normal temperatures will continue through early next
  week, with near normal temperatures returning mid week

&&

.DISCUSSION...Water vapor imagery tonight shows an upper level
closed low over the PacNW, with the center of the low poised to
move inland along the central OR coast. Meanwhile, nighttime
satellite imagery shows cloudy conditions mainly across the
Cascade east slopes, central OR, and the eastern mountains with
clear to partly cloudy skies elsewhere. Though cloud cover is
present, regional radar shows rain showers mainly outside of the
forecast area, though a few light showers are moving over the
Strawberry mountains and the southern Elkhorn crest.

The PacNW will continue to be under the influence of the upper
closed low through early next week, with persistent rain chances
(rain/snow mix above 7.5kft) over the mountain zones. Afternoon
temperatures across the region will be nearly 10-15 degrees below
average each day, with afternoon high temperatures at their lowest
in the mid 60s to mid 70s today (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
Saturday before sliding east Sunday into Monday(confidence 80-90%).
During this time, persistent rain shower chances (35-75%) will
remain over the Cascades and eastern mountains each day, with
shortwave impulses Friday/Saturday and the low passage Sunday/Monday
producing light rain chances (15-40%) in the lower elevations.
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.

Sunday into Monday, ensemble and deterministic members show the
upper closed low beginning to push east, with the low over the
forecast area during the day Sunday. While light to moderate rain
showers are forecast across the area, the upper low being overhead
and weak instability developing at the surface will also result in
slight chances (15-25%) of isolated thunderstorms focused across the
central OR Cascades and the eastern mountains Sunday afternoon and
evening. 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 within an area of split flow (confidence 55-65%).
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, however there is
spread in the location of the low amongst ensemble solutions.
Solutions (25% of cluster members) with the low offshore the OR/CA
border favor light showers along the OR Cascade crest and Ochoco-
John Day Highlands, while solutions (69% of cluster members) with
the low further south favor dry conditions persisting.

Spread in the evolution of the cut-off low only grows Thursday as
members are split in timing, location, and strength of the low.
Solutions (53% of members) that have the low become an open wave and
approach the PacNW favor the return of widespread unsettled weather
conditions, while remaining solutions (47% of members) favor a
trough evolution that results in dry conditions across the forecast
area. Confidence in forecast details is low (15-20%) for the mid-
week period. Lawhorn/82
&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...Mainly VFR
conditions are expected through the period. However, if there is
a heavy shower or thunderstorm that affects any TAF site than
MVFR (or possibly lower) can briefly occur. IFR conditions
should be 20% or less. Winds will generally be 10 kts or less.


&&

.Preliminary Point Temps/PoPs...
PDT  71  42  69  45 /  10  10  40   0
ALW  72  48  71  49 /  30  10  30  10
PSC  74  45  73  45 /  10  10  30   0
YKM  73  47  71  47 /  10  10  30  10
HRI  74  45  72  45 /  10  10  40   0
ELN  69  41  68  42 /  20  10  40  10
RDM  64  34  67  37 /  50  60  10  40
LGD  68  40  71  41 /  40  20  50  10
GCD  68  40  70  41 /  20  30  40   0
DLS  75  51  74  52 /  20  20  50  30

&&

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

&&

$$

DISCUSSION...82
AVIATION...77