516 
FXUS66 KPDT 101034
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
334 AM PDT Thu Sep 10 2026

.KEY MESSAGES...

- Breezy winds and dry conditions today - Elevated Fire Weather 

- Isolated thunderstorms Saturday

- Widespread showers Saturday through Sunday morning

&&

.DISCUSSION...

SHORT TERM
Current radar and infrared satellite imagery shows dry
conditions as high level clouds stream across the Kittitas
Valley and into the Columbia Basin from the north. This is in
response to an approaching upper level trough and associated
weak cold front that will move into the area this afternoon. 
The system will provide an increase in cloud cover, slightly 
cooler afternoon temperatures, light evening showers over the
northern Blue Mountains/foothills, and breezy conditions across
the Columbia Gorge, Simcoe Highlands, and the Kittitas Valley.
The overall trend in both the light rainfall and breezy winds
have decreased over the past 24 to 48 hours as guidance has
trended toward a weaker cold front, upper level shortwave, and
pressure gradient developing along the Cascades. Sustained
west-northwest winds of 15-25 mph with gusts of up to 40 mph
will be possible across the aforementioned areas, with gusts of
20-25 mph expected over lower elevations of the Columbia Basin,
Blue Mountain foothills, and Central Oregon. Winds peak between
1PM and 5 PM. Advisory-level winds are not anticipated as the 
NBM suggests only a 6% chance across Ellensburg, which is down 
from 9% yesterday and 22% on Tuesday. However, fire weather 
concerns arise as afternoon humidities are projected to drop 
back into the mid-teens across Central Oregon and the John Day 
Basin. Winds are expected to be just shy of critical values at 
lower elevations where humidities are lowest, but may still lead
to fire spread concerns through the afternoon and early 
evening. Due to the present dry airmass, rain amounts are 
expected to be minimal and only 0.01-0.05" at higher elevations 
through the Blue Mountains after 5PM. The HREF and NBM both 
highlight a 10-30% chance of measurable rainfall (0.01") over 
these areas, with highest amounts in and around the Tollgate 
area.

The trough broadens tonight into Friday morning as a strong
upper level shortwave pushes offshore just north of Vancouver
Island and strengthens to a low pressure system as it continues
its descent. It reaches the Washington and Oregon coasts early 
Saturday before moving onshore and into the region Saturday 
evening into Sunday morning. The developing southwest flow and 
efficient moisture supply from another closed low pressure 
system located in the Eastern Pacific, will initiate showers 
along the Cascade and eastern mountains Saturday afternoon 
before becoming widespread after 5PM. Guidance is in good 
agreement with this feature, and has trended slower and wetter 
in the previous 24-48 hours - which is directly related to the 
strength of the closed low over the Eastern Pacific. This slower
progression of the incoming system will provide a slight gap 
between this system and the exiting system bringing today's 
breezy conditions to the area. This gap will allow a transient 
ridge of high pressure to develop between these two systems, 
which will keep humidities at lower elevations rather dry and in
the 30-40% range early Saturday afternoon. As a result, rain 
amounts across lower elevations of the Columbia Basin/Gorge, 
Central Oregon, and Blue Mountain foothills may struggle to 
reach a wetting rain (0.10" or greater). Higher elevations are 
expected to receive a wetting rain (60-70% chance via the NBM), 
with up to 0.50" over the Cascade crest and Wallowa county. The 
developing ridge will also lead to the potential for isolated 
thunderstorms to develop through the afternoon and evening 
across the east slopes of the Cascades, John Day Basin, and the 
Blue Mountains (15-25% chance). The main thunderstorm concerns 
include gusty outflow winds, frequent lightning, and brief 
downpours as both the AI ECWMF and GFS ensembles suggest 
precipitable water amounts of 0.88-0.98" - which is 125-155% of 
normal. 75
  

LONG TERM
During the day on Sunday, models are in good 
agreement that rain chances will start to decrease throughout 
the day as the closed upper low moves into the region. Latest 
LREF clusters show that this solution is supported by around 75%
of the members. Due to the slowing trend mentioned earlier, the
precip will likely linger through the morning hours and into 
the afternoon. Current NBM probabilities for measurable precip 
(>0.01 in) during the morning are highest in the Blue and the 
Wallowa Mountains with probabilities between 70-80%. Elsewhere 
in the CWA, probabilities are generally between 40-50%. The 
exception is in the lee of the Cascades south of I-84, where the
NBM has probabilities between 5-20%. Most of the region will 
have a good chance of seeing a wetting rain (>0.1in) from this 
system with probabilities from the NBM between 50-60% for lower 
elevations and 80-90% in higher elevations. Latest model 
guidance does develop very small amounts of instability during 
the day on Sunday over the higher terrain so an isolated 
thunderstorm could develop (10-20%).

It is worth noting that there has been an increase in support since 
the last run of the LREF for an outlier scenario where the trough 
doesn't come ashore until midday Sunday. Currently only around 12% 
of the members support this solution (The vast majority of them come 
from the GEPS ensemble). In this solution, the rain chances don't 
come in until Sunday (Instead of Saturday) and the overall 
QPF amounts are lower. 

After Sunday, models indicate weak large scale troughing to be 
present with the possibility of a weak cutoff low forming off the 
coast of California. However, given the quiet nature of the upper-
level flow, impacts seem limited at this time with temperatures 
running around or slightly below normal (1-6F).

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
VFR conditions currently across all sites, which will stay the
course through the period. An incoming system will lead to
breezy winds of 15-25kts across most sites, and increasing  
broken to overcast cloud cover with ceilings of 25kft this
afternoon and evening. Winds should taper off as clouds slowly
break toward the end of the period. 75

&&

.Preliminary Point Temps/PoPs...
PDT  84  48  72  49 /   0  20   0   0 
ALW  84  54  73  53 /   0  10   0   0 
PSC  87  52  76  50 /   0   0   0   0 
YKM  82  50  71  52 /   0   0   0   0 
HRI  87  52  76  49 /   0  10   0   0 
ELN  74  46  68  47 /   0   0   0   0 
RDM  85  44  74  40 /   0   0   0   0 
LGD  86  48  75  45 /   0  20   0   0 
GCD  86  49  76  47 /   0   0   0   0 
DLS  83  54  75  54 /   0   0   0   0 

&&

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

&&

$$

SHORT TERM...75
LONG TERM...26
AVIATION...75