137
FXUS66 KPDT 200517
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
1017 PM PDT Sat Sep 19 2026

.KEY MESSAGES...
- Warming and drying trend through Monday.

- Chance for mountain showers toward end of the week.

&&

.DISCUSSION...
Current radar and visible satellite imagery shows dry conditions
under mostly clear skies. This is in response to an upper level
ridge axis centered over the Pacific Northwest. The ridge will
continue to slowly track east, which enhances southwest flow
aloft to allow for warmer air to advect into the region.
Slightly above normal temperatures will result this afternoon as
highs will reach into the upper 70s to low 80s across the
Columbia Basin, Blue Mountain foothills, and Central Oregon. The
warming trend persists on Sunday with highs in the mid-80s,
peaking on Monday with afternoon temperatures reaching into the
upper 80s across the aforementioned areas. Minimum humidities
will also be on the decline during this timeframe, dropping into
the mid- to upper teens across portions of Central Oregon and
the John Day Basin Sunday and Monday. The trend shifts on
Tuesday to cooler and more moist, which is associated with an
upper level shortwave moving onshore over the central British
Columbia coast. This trend will be slow and steady as high
temperatures tick down 2-4 degrees each day through the
remainder of the week. The improvement of humidities will lag
slightly and trend slower, eventually staying in the low to
mid-20s on Friday in relation to a second and more robust
approaching system.

The first shortwave on Tuesday will struggle to dig into the
Pacific Northwest due to the incumbent and slowly departing
ridge of high pressure. Guidance strongly suggests the area
staying dry as the system passes, with only 48% of ensemble
members hinting at rain chances only over the John Day
Highlands. The upper level ridge will rebuild slightly Wednesday
and early Thursday ahead of the next system late Thursday into
Friday. Guidance disagrees with the timing and strength of this
system, which is expected to weaken quickly on its approach
to the southern British Columbia and northern Washington
coasts. Ensembles advertise light mountain showers beginning
Thursday afternoon across the Cascades, with 56% of members
suggesting widespread light showers Thursday night into Friday
morning due to a stronger and earlier arriving system. Just 24
hours ago, it was the consensus that the system will be slower
and keep showers more confined to the Cascade and Blue
Mountains. The NBM is aligning more with the latter scenario of
primarily dry lower elevations and 0.01-0.05" at higher
elevations across our mountain zones. Due to the overall low
confidence, the shifting of ensemble consensus from a slightly
wetter to drier outcome over subsequent model runs is expected
over the next 24 to 48 hours, with the primary outcome likely to
align with light showers and minimal weather impacts. 75

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
VFR conditions will persist through the forecasted period. Winds
will be diurnally driven and below 12 kts. High clouds will
linger over DLS/PSC, otherwise SKC.

&&

.Preliminary Point Temps/PoPs...
PDT  49  83  50  84 /   0   0   0   0
ALW  54  85  56  85 /   0   0   0   0
PSC  52  86  52  87 /   0   0   0   0
YKM  54  84  54  85 /   0   0   0   0
HRI  51  85  53  86 /   0   0   0   0
ELN  52  79  52  80 /   0   0   0   0
RDM  43  84  45  84 /   0   0   0   0
LGD  49  83  51  84 /   0   0   0   0
GCD  49  84  50  85 /   0   0   0   0
DLS  57  88  59  86 /   0   0   0   0

&&

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

&&

$$

DISCUSSION...75
AVIATION...90