966
FXUS66 KPDT 261120
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
420 AM PDT Thu Sep 26 2024

.SHORT TERM...Today through Saturday night...

Key Messages:

1. Showers return to the Washington Cascades tonight into Friday.

2. Breezy winds tonight through Friday.

3. Above normal temperatures persist into the weekend.

Current radar and infrared satellite imagery shows light returns
exiting east Wallowa county and lingering over Snoqualmie Pass
under clearing skies. This is a result of the departing upper
level trough and associated cold front that will continue to
depart to our northeast and into southern Alberta by mid-morning
on Thursday. In the wake of this system, upper level high pressure
over the Desert Southwest will encroach into the Northern Rockies
today and Friday to provide zonal flow over the area. The
building high pressure will help to deflect a weak, incoming
shortwave later this afternoon and evening, leading to rain
chances (35-65%) being confined along the Washington Cascade crest
as rain amounts of 0.10-0.20" are expected over Snoqualmie Pass
between 5PM tonight and 5AM Friday morning. Rain accumulations
will stay fairly well confined to the Cascade Crest as only a
trace is expected at Cle Elum and dry conditions at lower
elevations. Confidence in these rain amounts are high (80-90%) as
the HREF and NBM both highlight a 60-70% of 0.10" or greater rain
amounts at Snoqualmie Pass, dropping to a 40-50% chance of 0.20"
or greater rain amounts.

The weak shortwave and associated cold front will pass over the
area this evening and into early Friday morning, also attributing
to elevated winds along the east slopes of the Washington
Cascades and Simcoe Highlands. Sustained winds of 10-20 mph will
be possible with gusts of up to 30 mph out of the west, peaking
between 11PM Thursday and 5AM Friday. Confidence in these elevated
winds is high (80%) as the HREF and NBM both advertise a 70-90%
chance of wind gusts of 30 mph or greater and a 60-70% chance of
sustained winds of 20 mph over the aforementioned areas. In the
wake of this passing weak cold front, a pressure gradient looks to
set up Friday afternoon over the Kittitas Valley as suggested by
a 4.5-7 mb difference between Everett (PAE) and Pasco (PSC) via
the GFS, NAM, and SREF. These values correlate to sustained winds
of 15-20 mph and gusts up to 30 mph out of the west, peaking
between 2PM and 8PM on Friday. Confidence in these wind values is
moderate (60%) as the HREF and NBM suggest a 65-75% chance of
sustained winds of 20 mph or greater with only the NBM showing a
67% chance of gusts reaching 30 mph or greater.

Persistent west-southwest flow aloft into the early part of the
weekend will keep temperatures above normal as highs stay in the
upper 70s to low 80s across lower elevations of the Basin.
Temperatures are expected to slowly increase into Saturday as flow
aloft incurs more of a southerly component due to an approaching
shortwave. Near normal high temperatures today will become 5-7
degrees above normal Friday and 6-8 degrees above normal on
Saturday. Confidence in highs reaching into the low 80s for areas
of the Basin is moderate (60-70%) as the NBM highlights a 45-65%
chance of 80 degrees high temperatures on Friday and Saturday for
Hermiston, Walla Walla, Pilot Rock, and the Tri-Cities.
Temperatures do look to return to near normal over the beginning
part of the week. 75


.LONG TERM...Sunday through Thursday...

Model are in good agreement with the shortwave trough moving into
the PacNW Sunday. With increased west-northwesterly flow, gusty
winds will develop at 20-30 mph (60-90% probability) at the Kittitas
and Yakima Valley including eastern CR gorge. As the trough moves
eastward, a upper ridge builds over into the region Monday with
winds less than 12 mph (>70% confidence). No major weather impacts
will occur for these days.

Slight chances (15-30%) of showers could occur Tuesday at the WA
Cascades due to the orographic lifting from the cold front. Models
are in good agreement with the cold front arriving to the PacNW
Tuesday. Wednesday will have breezy winds up to 20 mph as the upper
ridge moves inland of the region off OR coast. WA Cascades might
have developing showers, but chances are low (<20%) as the upper
ridge builds over off OR coast.

The PacNW will enter a ridge Thursday with slight chances of evening
showers at the WA/OR Cascades. For Thursday night, about 32% total
cluster members favor a ridge breakdown whereas 51% members has a
ridge over the PacNW with only 18% members favoring a zonal pattern.
If the ridge breaks down, chances of showers could increase. But if
not, then a upper ridge may stay longer thus returning dry
conditions and warm temps. Unfortunately, this can make this weather
pattern challenging to forecast, given the uncertainties. Feaster/97


&&

.AVIATION...12Z TAFS...VFR conditions are expected through the
TAF period. Mid to high (FEW-BKN at 070-250) clouds will prevail
for the next 24 hours. Winds will be less then 12 kts. Feaster/97



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  72  48  77  47 /   0   0   0   0
ALW  74  53  79  51 /   0   0   0   0
PSC  75  56  80  50 /   0   0   0   0
YKM  72  48  77  44 /   0   0   0   0
HRI  75  52  80  49 /   0   0   0   0
ELN  70  49  73  44 /   0   0   0   0
RDM  76  43  79  43 /   0   0   0   0
LGD  74  48  79  48 /   0   0   0   0
GCD  77  48  84  50 /   0   0   0   0
DLS  77  54  80  52 /   0   0   0   0

&&

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

$$

SHORT TERM...75
LONG TERM....97
AVIATION...97