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000
FXUS66 KPDT 221131
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
431 AM PDT Mon Apr 22 2024

.SHORT TERM...Today through Wednesday...Current radar shows not
a thing happening over the CWA along with nighttime satellite
imagery is showing mostly clear skies with some high thin cirrus
lingering around Deschutes, Crook and Grant counties. With the
exception of the nearly full moon, it is a perfect night for
watching the Lyrid meteor shower to the northeast.

The short term will be dominated by an upper level ridge through
early Wednesday. Dry conditions will linger through Tuesday night
before an upper level trough makes its way onshore. Precipitation
will return to the mountains while the remainder of the CWA will
remain dry.

Models are in relatively good agreement today through Tuesday
afternoon with the upper level ridge remaining overhead.
Conditions will remain dry with mild temperatures across the area.
63% of the raw ensembles show temperatures to be in the low to
mid 60s for the majority of the lower and highland elevations with
over 50% showing the higher elevations around Ellensburg and
Meacham seeing high 40s to low 50s. Tuesday will be the warmest
day of the period with temperatures will be 2-5 degrees warmer
with over 60% of the raw ensembles showing the foothills of the
Blues in the mid to upper 60s, 50% show the Basin, Gorge and
adjacent valleys in the upper 60s to low 70s, over 60% show
central and north central OR in the upper 60s to low 70s, and
lastly, 50% show the higher terrains in the upper 50s to low 60s.

Models remain in good agreement with the incoming trough with the
clusters showing the main variances being with the amplitude of
the incoming trough. Deterministic guidance also shows a timing
variance with the onset of the incoming precipitation. GFS has the
precipitation reaching the WA Cascades early Wednesday morning,
while the Euro has it arriving in the afternoon. Regardless of
timing, 50-80% of the raw ensembles show 0.01 inches of rain to
fall across the WA Cascades with POPs between 20-35%. Temperatures
will decrease by 2-5 degrees and winds will increase due to the
trough. Deterministic guidance shows a tightening of the pressure
gradients across the Cascades as the trough moves over the
mountains. NBM ensembles show 60-80% chance the Gorge, Simcoe
Highlands and portions of the lower Columbia Basin will see
sustained winds of 22 kts and gusts to 34 kts Wednesday night.
Bennese/90


.LONG TERM...Thursday through Friday...An upper trough will be over
PacNW as a cold front arrives with widespread precip Thursday.
Friday into Saturday morning, precip lingers whereas the trough
deepens but begins tapering off when PacNW is in between systems.
Rain is expected with a 30-50% chance at the low elevations and a
50-60% chance at the crest of the Cascades Thursday morning, but
<10% chance for Lower Columbia Basin of Washington. Chances of
precip increases Friday when the cold front moves over the PacNW
but decreases again Friday night into Saturday morning once the
forecast area enters between systems (50-70% confidence).

The cold front will bring moisture and enhance lift for
thunderstorms to develop Friday late morning into the afternoon over
the Blue Mountains and John Day Basin, but with a slim chance (15-
30%) due to low CAPE values. There seems to be a decent agreement
with the occurrence of the trough over the PacNW Thursday but the depth
and position differs onwards. 43% of GFS members favor the trough
axis shifted more eastward and shallower, whereas the GFS shows it
as slightly deeper and more West for Friday. For Saturday, the GFS
shows the PacNW in between systems but other models have it in a
trough.

Clusters favors the trough over PacNW overall but has uncertainties
within the depth are present There is good agreement on the
troughing position shifting southeasterly. However, about 51%
members favors a shallower trough over The Rockies but more of a
zonal pattern over PacNW. Only 49% members agree on the rough
deepening over The Rockies. It is difficult to forecast the precip
due to not knowing how this trough will behave, lowering confidence
in this weather pattern (30-40%). Simcoe Highlands and Central OR
will be gusty at around 20-30 kts Thursday and Friday as the systems
move over the region (>50% confidence). Temperatures remains near to
above normal through the period. Feaster/97


Saturday through Monday...Guidance is in good agreement
in the overall synoptic pattern over the weekend into early next
week, with west-southwest flow aloft likely persisting. This is in
response to an upper level low tracking through the Four Corners
area as another slowly approaches the British Columbia coast.
However, there are wide differences in both deterministic and
ensemble solutions regarding timing, strength, and location of these
synoptic features, which relate to differing rain chances,
temperatures, and winds that can be expected during this timeframe.
The primary weather concern resides with breezy conditions across
the Basin, east slopes of the Cascades, Eastern Gorge, and the
Simcoe Highlands Sunday afternoon, with both the ECMWF and the GFS
highlighting elevated winds. Both are associated with an upper level
shortwave that spins off the parent upper level low, still located
off the southern British Columbia coast, but the low is much closer
in the ECMWF solution which would lead to breezier winds. This
closer upper low also provides more efficient moisture transport to
provide higher chances of precipitation and rain amounts, with
cooler high temperatures and slightly warmer overnight temperatures
due to increased cloud cover.

Sunday`s shortwave does look stronger due to the proximity of the
parent system, which leads to a higher potential for winds. Wind
gusts of 15 to 25 mph are expected on Saturday afternoon, bumping up
to 25-35 mph Sunday afternoon. Precipitation chances look to stay
confined to areas at elevation over the Cascades and eastern
mountains each day, peaking through the afternoon. Snow levels are
consistent through the period between 4000 and 5000 feet, so any
snowfall will only occur at higher terrain and stay below an inch.
Rain amounts will stay below 0.10 of an inch each day, confined to
areas above 4000 feet along the Cascades and above 2500 feet across
the northern Blue Mountains. A weak transient shortwave overnight
into Sunday morning looks to provide a brief respite in
precipitation before the second shortwave passes through the area.
High temperatures are expected to stay near or just below normal for
this time of year, which is in the upper 60s to low 70s.

West to southwest flow aloft is suggested by 73% of ensemble members
over the weekend, which align more with the ECMWF solution of more
efficient moisture transport than the GFS. Analyzing the strength
and arrival of the trough is a little less clear cut, with 60-70% of
ensemble members leaning toward a later arrival and stronger
approaching low - which 52% of ensembles were expecting the opposite
to occur just 12 hours ago. Due to these discrepancies, confidence
is moderate (50-60%) regarding mountain showers, moderate (40-50%)
for elevated afternoon winds, and low to moderate (30-50%) for below
normal high temperatures each day. Thus, the NBM was utilized to
provide an applicably weighted scenario. 75

&&

.AVIATION...06Z TAFs...Skies will clear and winds will diminish
tonight.  Winds on Monday will be 10kt or less and skies will be SCT-
BKN AOA 20kft.  Wister/85


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  61  36  66  42 /   0   0   0   0
ALW  64  38  68  45 /   0   0   0   0
PSC  67  40  70  44 /   0   0   0   0
YKM  66  37  69  41 /   0   0   0   0
HRI  66  38  70  44 /   0   0   0   0
ELN  63  36  66  44 /   0   0   0   0
RDM  65  34  68  36 /   0   0   0   0
LGD  61  34  68  41 /   0   0   0   0
GCD  66  36  71  41 /   0   0   0   0
DLS  68  44  71  46 /   0   0   0   0

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...Freeze Warning until 9 AM PDT this morning for WAZ026-027.

&&

$$

SHORT TERM...90
LONG TERM....75/97
AVIATION...85