983 
FXUS66 KPDT 281143
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
443 AM PDT Sun Sep 28 2025

.Updated Aviation Discussion.



.AVIATION...12Z TAFS...VFR conditions currently across all sites,
which will stay the course through the period. Light winds below 
10 kts will persist, with KRDM/KBDN being the exception as winds 
will hover around 10 kts this afternoon. Cloud cover will increase
in the evening as a system approaches from the west, with 
ceilings of 25kft. 75


&&


PREV DISCUSSION... /issued 341 AM PDT Sun Sep 28 2025/ 

DISCUSSION...

Key Messages:

1. Warm and dry day ahead.

2. Showers and isolated thunderstorm threat through week. 

Current radar and infrared satellite imagery shows dry conditions
as a thin veil of high level clouds slowly cross through the area.
This is in response to the incumbent ridge slowly beginning to 
depart to our east as an upper level trough approaches the coast 
later today. Southwest flow aloft will enhance today to provide a
slightly warmer day with highs peaking in the low to mid-80s 
across the Columbia Basin and lower elevations of Central Oregon. 
These values are about 10 degrees above normal for this time of 
year, which will also be coupled with afternoon humidities dipping
down between 15-25%. Lower humidity values are expected to occur 
across the John Day Basin, Northern Blue Mountains/Foothills, 
Grande Ronde Valley, and lower elevations (<4500') of Wallowa 
County. Confidence in these areas experiencing humidities below 
20% is high as the HREF suggests a 70-90% chance of occurrence. 
Winds will be slightly more elevated today as a pressure gradient 
develops along the Cascades. The NAM, SREF, and GFS all advertise 
a pressure gradient of 4.3-4.9 mb between Medford (MFR) and 
Pendleton (PDT), which corresponds to sustained winds of 10-15 mph
with gusts up to 20 mph across Central Oregon. The HREF is in 
alignment with these winds, highlighting a 65-85% chance of winds 
reaching 15 mph or above and gusts of 20 mph or higher east of the
La Pine/Bend area between 2-5 PM. Elevated winds of 10-15 mph 
with gusts of 20 mph are also expected through the Columbia Gorge,
Simcoe Highlands, and the through the Cascade gaps west of Yakima
as the GFS, NAM, and SREF also show a 3-3.5 mb pressure gradient 
developing between Portland (PDX) and Hermiston (HRI). Confidence 
in these winds is not as strong as across Central Oregon, with the
NBM suggesting a 40-50% chance of sustained winds of 15 mph or 
greater with a 45-65% chance of gusts of 20 mph or greater. These 
winds will be occurring in areas of improved humidities from 
Saturday, leading to minimal fire weather concerns.

Clouds will increase this evening and into Monday as rain chances
(20-40%) begin to spill over the Cascade crest and extend into the
eastern slopes. Showers become widespread by late afternoon and
evening as the upper level trough moves onshore and the associated
cold front slowly passes through the Columbia Basin into Tuesday
morning. This trough is one of many that will be passing through
the Pacific Northwest through the week, as a strong upper level
low pressure system drops from the Gulf of Alaska Monday and
approaches the coast later in the week. However, this first trough
looks to be the most efficient at bringing widespread rain amounts 
across the region as it taps into subtropical moisture from the 
25-30N latitudes. As a result, a wetting rain (=>0.10") is 
anticipated to occur through much of the area (40-60% chance via 
NBM) with the exception of the Tri-Cities area (24%) and Yakima 
(31%). The highest rain amounts of around 0.20" will occur over 
the John Day Highlands and the northern Blue Mountains with 50-60%
confidence. Rain amounts Tuesday and Wednesday will struggle to 
reach wetting rain amounts outside of the Cascade crest, east 
slopes of the Cascades, Elkhorns, and higher elevations of the 
Blue Mountains. 

The incoming system will also bring with it the chance for
isolated thunderstorms as it erodes the backside of the upper
level ridge. The best chances will occur along the east slopes of
the Oregon Cascades into the US-97 corridor and across Grant,
Union, and Wallowa counties as the NAM advertises 100-200 J/kg of
surface CAPE. The NAM also hints at this same amount of CAPE over
Wallowa County on Tuesday afternoon, and the GFS shows 50-150 J/kg
of CAPE across the Cascades, Columbia Basin, and the northern Blue
Mountains/Foothills on Wednesday. At this time, Wednesday does
look to have more of a widespread thunderstorm threat, however,
models and ensembles are in disagreement on the timing and
progression of the upper level low pressure as it moves onshore.
Currently, ensemble members are split between the low opening up
and moving inland along the British Columbia coast Wednesday or
pushing onshore along the Oregon/California coasts late Thursday.
Currently, the former scenario is the front-runner, which would 
lead to a better potential for isolated thunderstorms as 
additional CAPE would be available. Even with the potential for 
afternoon thunderstorms, they are expected to stay discrete and 
sub-severe (<10% chance of severe storms). 75

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  83  53  78  53 /   0  10  20  60 
ALW  83  58  79  58 /   0  10  10  60 
PSC  83  53  78  54 /   0   0  10  50 
YKM  82  55  76  51 /   0  10  20  50 
HRI  83  54  79  54 /   0  10  20  50 
ELN  80  51  73  48 /   0  20  30  60 
RDM  84  49  73  42 /   0  10  40  60 
LGD  86  53  77  52 /   0  10  20  80 
GCD  86  52  75  48 /   0  10  40  80 
DLS  84  59  76  55 /   0  10  40  60 

&&

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

$$

SHORT TERM...75
LONG TERM....75
AVIATION...75