848
FXUS66 KPDT 262203
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
303 PM PDT Fri Apr 26 2024

.SHORT TERM...Today through Sunday...Current radar is showing a
few showers popping up over the Ochoco-John Day Highlands and
along portions of the Northern Blues and Wallowas. Observations
over the last our shows that a few locations along the east slopes
of the Cascades have received 0.01- 0.05 inches of precipitation.
Portions of the Ochoco-John Day Highlands have seen 0.02-0.04
inches and the Wallowas have seen around 0.06 inches so far.
Current satellite shows scattered clouds across the Basin and
adjacent valleys as well as along the eastern mountains with
embedded showers. Temperatures today will remain seasonal with the
lower elevations seeing temperatures in the mid to high 60s, mid
elevations seeing the mid to upper 50s and the highest elevations
in the low to mid 40s.

Today the models remain in form agreement with the upper level low
being mostly overhead and essentially straddling the region with the
center of the low a bit to the south east. With he cold core to the
southeast and upper level winds mostly southwesterly, orographic
lift could help initiate some pulse thunderstorms over the eastern
mountains. CAMs models show MUCAPE values to continue to be in the
250-350 J/kg with a few areas in Grant County showing values above
500 J/kg range with lapse rate around 7.2-7.4 C/km and effective
bulk shear only in the 15-20 knot range. While some of these needed
ingredients are weak, there is still a enough of them to put out a
marginal possibility of 20-30% probabilities isolated thunderstorms
could pop up along the eastern m mountains with the CAMs models and
ensembles targeting Grant County with the highest probabilities,
again only 20-30%. EFI shows the CWA to be under seasonable
conditions with 70%raw ensembles having the PDT area in the low to
mid 60s, 90% have the Basin and adjacent valleys in the mid to upper
60s with isolated 70s, mid elevations in the mid to upper 50s.

Models over the weekend remain in firm agreement with the upper
level low moving off towards the southwest while another upper level
trough begins to meander to the south out of the Gulf of Alaska. The
region will shift into more of a westerly pattern and the concern
over the weekend will lean more towards the winds. While the
westerly flow will bring precipitation primarily to the mountains,
the system will also usher in a bit cooler temperature along the
Cascades bringing the snow levels a bit lower to around pass levels
increasing the chances of some snowfall along Snoqualmie Pass by
Sunday. Looking at the raw ensembles, 70-80% agree that there is
near an inch of snowfall probable along the WA Cascade and 50-70%
along the OR Cascades. Westerly flow will also cause an increase in
the winds, especially through the Cascade Gaps. NBM ensembles show
the 24 hour probability of max sustained winds of greater than 30
mph to be 60-90% probable through the Gorge, Columbia Basin, Simcoe
Highlands, Yakima and Kittitas valleys and through Union County with
some isolated pockets in central OR and along the eastern slopes.
EFI continues to show the temperatures over the weekend to be near
seasonal averages with the ensembles showing the lower elevations in
the mid to upper 60s, foothills in the upper 50s to low 60s, mid
elevations in the low to mid 50s and the higher elevations in the
low 40s. Bennese/90

.LONG TERM...Monday 12Z(Monday) to Saturday 00Z(Friday)...

A upper-level trough pattern associated with a broad low moves
southeasterly across BC coastline and then PacNW Monday into Tuesday
night. As the trough passes eastward to The Rockies, PacNW begins
entering a ridge Wednesday through the remainder of the forecast
period (50-60% confidence).

Both deterministic models and ensemble means have a good agreement
on the trough occurring Monday into Tuesday night, including the
arrival of an upper ridge Wednesday into Friday. However, there is a
uncertainty for Wednesday night with 21% total cluster members
favoring a trough whereas 61% total members show a ridge occurring
with the trough axis positioned in The Rockies. Thursday into Friday
shows a decent agreement with ridge moving over PacNW. Chances of
precip at the low elevations are low (<20%) with a 30-40% at the
mountain areas for Monday morning into night as the broad low passes
before precip starts to decrease when the ridge occurs. Gusty winds
will occur between 20-35 kts for Monday into Tuesday as the broad
low passes, influenced from the surface pressure gradient from the
troughing. Snow levels from Monday to Tuesday will decrease to 2000-
4000 ft as the trough passes through, but increases to 3000-6000 ft
with the ridge moving over PacNW enters between systems Wednesday
into Friday. Feaster/97


&&

.AVIATION...18Z TAFS...VFR for all sites with
cloudy skies (SCT to BKN, 040-120 kft) during this period. There
might be some vicinity showers for KRDM and KBDN through afternoon,
given the cold upper-level low passing over PacNW (50-60%
confidence). KBDN might experience gusty winds at 15-20 kts but
should decrease to light winds this evening. Otherwise, winds will
be light. Feaster/97


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  61  40  62 /  20   0   0   0
ALW  46  65  45  64 /  20   0   0   0
PSC  47  68  46  67 /   0   0   0   0
YKM  40  65  37  64 /  20  10   0   0
HRI  45  66  42  66 /   0   0   0   0
ELN  41  60  37  59 /  30  30   0   0
RDM  34  56  36  59 /  30  10   0   0
LGD  40  58  40  60 /  40  20  20   0
GCD  38  58  36  61 /  30  10  10   0
DLS  46  61  45  62 /  30  10   0   0

&&

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

$$

SHORT TERM...90
LONG TERM....97/86
AVIATION...97