Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 302234

Area Forecast Discussion
National Weather Service Pendleton OR
234 PM PST Mon Jan 30 2023

.SHORT TERM...TODAY THROUGH WEDNESDAY...Current radar and visible
satellite imagery showing dry conditions under clear to mostly
clear skies across the area. This is a result of the upper level
ridge, located over the Eastern Pacific, encroaching into our area
from the west. These clear conditions will be short-lived as a
weak, upper level shortwave will ride down the front side of the
upper level ridge to provide breezy conditions through the Grande
Ronde Valley and the Wallowa County, as well as a slight chance
for mountain snow showers along the Central Washington Cascade
crest, Northern Blue Mountains, and south/east Wallowa County
Tuesday. Winds will be increasing tonight into Tuesday as gusts of
30 to 40 mph will be possible through the Grande Ronde Valley
(especially through the Ladd and Pyles Canyons), peaking from late
morning through the early evening on Tuesday. Confidence is
moderate to high (50-70%) regarding these wind values as the
NBMv4.1 highlights a 60% chance of wind gusts reaching 39 mph, but
drops to only a 10% chance for gusts of 47 mph or above through
the Grande Ronde Valley. Expected snowfall will be rather minimum
through the aforementioned mountain areas during the morning and
early afternoon hours on Tuesday, with 1 to 2 inches possible
above 5000 feet over the Wallowa Mountains and one half inch or
less for higher elevations of the Northern Blue Mountains and the
Central Washington Cascades. Confidence is low to moderate
(20-40%) for these snow amounts, as the NBMv4.1 shows a meager 10%
chance of 0.1 inch in and around the Snoqualmie area and only a
2-5% chance of 0.1 inch over the Northern Blue Mountains.

The significant northerly flow aloft and associated deep ridge will
continue to suppress as a weak shortwave slides down the front
end of the ridge, effectively shifting flow aloft to more
northwesterly to provide warmer temperatures beginning Tuesday.
Cloud cover will also be increasing tonight north-to-south ahead
of the shortwave, which will help to keep overnight temperatures
in the upper-teens to low-20s into Tuesday morning. High
temperatures will be 5 to 10 degrees warmer on Tuesday than today,
with highs breaking into the upper 30s to low 40s across lower
elevations of the Basin and low to mid 40s through Central Oregon.
Winds will be breezy through the Grande Ronde Valley,
Southern/Eastern Wallowa County, Northern Blue Mountains, and
along the east slopes of the Cascades as the shortwave passes
through the area on Tuesday. The east slopes of the Cascades,
Blue Mountains, and Wallowa County will incur wind gusts of 10-20
mph through much of the day Tuesday and continuing into Wednesday.
Confidence is moderate to high (70-80%) regarding these gust
values with the NBMv4.1 showing an 80-90% chance of reaching 25
mph but only a 5-10% chance of reaching 39 mph over both days.
Very little moisture is associated with this weak feature, keeping
precipitation chances at higher elevations above 5000 feet
through the Washington Cascades, Northern Blues, and the Wallowa
Mountains. Lower elevations will merely experience partly to
mostly cloudy skies as a result of the passing shortwave. Flow
aloft will become more westerly into Wednesday as the ridge axis
slides east and into our area as an upper level trough digs south
from the Gulf of Alaska through the Northern Pacific. This will
help to keep temperatures on the upward climb with highs breaking
into the upper 30s to low 40s through the Lower Columbia Basin and
in the upper 40s to low 50s through Central Oregon. This will
also allow pressure gradients to tighten ahead of the incoming
system digging in the Pacific to allow for breezy conditions to
return at elevation over the eastern slopes of the Washington
Cascades and Northern Blue Mountains, especially through the
latter half of Wednesday. Winds will also stay breezy through the
Grande Ronde into Wednesday with gusts of 25 to 35 mph possible
out of the south. Confidence is moderate (60-70%) in these wind
gust amounts as the NBMv4.1 shows a 40-50% chance of gusts
reaching 39 mph and a 15% chance of gusts reaching 47 mph through
the Grande Ronde Valley. Winds look to stay elevated as
temperatures continue to climb as we proceed into the extended
period. 75

.LONG TERM...THURSDAY THROUGH MONDAY...Active weather looks to make
a return to the forecast area by the weekend, after we`ve undergone
a warming trend with high pressure overhead through most of the work
week. Another round of snow looks possible for our mountain zones
next weekend, as two shortwave troughs look to trek through the
PacNW Friday and Sunday.

High pressure slides out of the area by the end of Thursday before a
southwesterly trough injects more moisture into the interior
northwest. Gusty conditions are likely in the Grande Ronde Valley
Thursday (confidence >70%) as we transition from high pressure to a
shortwave, with focus shifting toward the precip threat heading into
next weekend. Ensembles in pretty good agreement on this pattern,
which would result in precip chances primarily for the mountains
Friday, as guidance leans toward this system being more on the
weaker end. Snow levels will be quite variable through the forecast
area, as warm air advection from the southwest will bump up the
Oregon Cascades closer to the 4000 ft range, while the Washington
Cascades remain cold with snow levels closer to 2000-2500 ft. Snow
levels over the eastern mountains look to be somewhere in between
2500-3500 ft, but QPF ensembles are vary sparse on precipitation
there for this first system. Bulk of precip threat looks to be in
the WA Cascades for Friday, with moderate confidence (40-60%) that
some form of pass-level snow will occur there next weekend.
Confidence decreases (20-30%) across our other mountain zones where
models are much lighter on precip. Ensembles largely keep the lower
elevations dry until next Sunday.

Cluster solutions are a bit more divided on Sunday`s system, but do
seem to lean towards the idea that this one will be a bit more
organized, thus leading to higher chances for area-wide precip. Much
could change between now and the next six days, but current guidance
puts confidence at 25-35% for lower-elevation and valley precip
Sunday, with mountain precip more in the 50-70% range. Current
thinking is that our non-mountain zones will have experienced enough
warming through the week to mix out any inversions and preclude cold
pooling, resulting in mostly a rain threat for next Sunday. NBM
currently suggesting snow levels >3200 ft for much of the forecast
area, but if SW flow leads this system as current global
deterministic guidance depicts, feel that this could be even higher
for areas such as central OR and the John Day/Ochoco Highlands.
Confidence is low (<20%) on potential amounts, but the next threat
of area-wide sensible weather looks to be associated with this
system next Sunday.

Warmer conditions will prevail as a result of high pressure followed
by SW flow over next weekend. Highs look to be in the 50s by the end
of the period for our population centers, with near-normal overnight
lows around freezing for all areas. Evans/74


.AVIATION...00z TAFs...VFR conditions expected through the next
24 hours. Some light mid-level clouds may build in this evening,
but otherwise quiet conditions expected with terrain-driven winds
less than 10 kts through the period. Evans/74


PDT  19  39  27  43 /   0  10   0   0
ALW  21  38  26  43 /   0  10   0   0
PSC  23  37  26  39 /   0  10   0   0
YKM  18  35  22  37 /   0  10   0   0
HRI  22  37  26  41 /   0  10   0   0
ELN  18  33  22  36 /   0  10   0   0
RDM  16  45  27  50 /   0   0   0   0
LGD  16  29  22  34 /   0  10   0   0
GCD  13  38  23  43 /   0  10   0   0
DLS  24  41  30  45 /   0   0   0   0




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