532
FXUS66 KPDT 232128
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
228 PM PDT Mon Sep 23 2024

.SHORT TERM...Today through Wednesday...

Bottom Line Up Front

1. Dry and warm conditions through mid week

2. Breezy conditions Wednesday

3. Chances of widespread precipitation Wednesday

Models are in firm agreement with the upper level ridge moving in
over the region today. With the ridge will come increased
temperatures across the region with at or slightly above near normal
temperatures with the highest temperatures occurring Tuesday. With
the amplitude of the ridge tilted and slightly flattened, models
show the majority of the warm temperatures will be centered around
the axis of the ridge which happens to be over central OR. Roughly
72% of the raw ensembles show central OR to be in the low 90s
Tuesday. Models have also highlighted central OR with moderate
HeatRisk due to the high daytime temperatures coupled with the
overnight highs remaining elevated overnight.

Models show that on Wednesday an upper level trough will slip down
the Canadian coast and move towards the PacNW. Surface pressure
models show a tightening of the pressure gradient along the Cascades
with a shortwave embedded within it. This will bring enhanced winds
through the Cascade Gaps as well as spill out across the entire CWA.
Looking at the probabilities of 25 mph or greater winds across the
area, dang near the entire region, minus Wallowa, will see 80-100%
probabilities of sustained winds of 25 mph or greater. Looking at
the probabilities of 39 mph or greater, the zones that show the best
promise, over 80% probabilities, are the Simcoe Highlands, foothills
of the Southern Blues, Yakima and Kittitas Valleys. Very isolated
pockets will see winds above that and there are currently no
advisories in effect as it remains below criteria.

Not only do the models show the upper level trough moving over, it
also shows a tail of moisture following along with it. However,
models do show some timing and amount differences. Blended a few of
the models together to achieve the forecasted amounts for Wednesday;
Raw ensembles show 80-100% probabilities of 0.1-0.3 inches of rain
along the crests, 30-50% probabilities of 0.05-0.1 inches for the
east slopes of the Cascades, 30-40% for 0.03 inches for the Blue
Mountains and 30-40% of the raw ensembles show the Gorge, foothills
of the Blues and the Columbia Basin will see up to 0.01-0.3 inches
of rain. Bennese/90

.LONG TERM...Thursday through Monday...Ensemble NWP models are in
very good to excellent agreement that a weak frontal system will
impact the Washington Cascades late Thursday through Friday morning.
Confidence in measurable light rain is medium-high (50-70%), with
lower (30-50%) chances of a wetting rain (0.10" or greater).
Elsewhere, chances of rain are very low (<15%).

Friday through Saturday morning, confidence is high (>70% chance)
that dry conditions will prevail with quasi-zonal flow aloft.

Saturday afternoon through Sunday, ensemble clusters suggest
increasing uncertainty in the 500-mb pattern over the PacNW; roughly
40% advertise a shortwave trough of varying amplitude, while the
remainder suggest an upper-level ridge extending northward into
Canada.

Monday, the favored solution is an upper-level ridge over the PacNW
and Intermountain West (44% of members), while 23% of members keep
the ridge axis centered just offshore. The remaining cluster
solutions show either a deep upper low digging across the
Intermountain West (8%) or a 500-mb zonal jet extending
into the PacNW with our CWA on the southern (warm) side.

Whichever solution verifies, ensemble agreement in any
climatologically unusual weather events is low per the ECMWF EFI.
Plunkett/86


&&

.AVIATION...18Z TAFs...VFR conditions are forecast for all sites
through the TAF period, with low chances (<30%) of smoke/haze
reducing CIGs/VSBYs to sub-VFR again overnight into Tuesday
morning at BDN/RDM. Otherwise, predominantly FEW-BKN high-level
clouds through the day, becoming SKC to FEW250 overnight through
Tuesday at TAF sites. Sustained winds of 10 kts or less,
diurnally driven for all sites. Plunkett/86


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  54  88  58  83 /   0   0   0  10
ALW  56  90  63  87 /   0   0   0  20
PSC  57  88  61  87 /   0   0   0  10
YKM  54  87  55  81 /   0   0   0  30
HRI  56  90  59  85 /   0   0   0  10
ELN  55  88  56  78 /   0   0   0  30
RDM  49  91  53  81 /   0   0   0  10
LGD  49  86  57  87 /   0   0   0  10
GCD  50  86  54  85 /   0   0   0  10
DLS  59  93  61  78 /   0   0   0  30

&&

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

$$

SHORT TERM...90
LONG TERM....86
AVIATION...86