Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 251619
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
919 AM PDT Mon Mar 25 2024

.MORNING UPDATE...Satellite and radar imagery this morning shows a
weakening cold front and weak upper shortwave pushing across
western OR/WA, with mid to high level cloud cover pushing ahead of
it in central OR. Elsewhere, mostly clear skies in the Columbia
Basin and low to mid stratus layers continue over the eastern
mountains. Today, the aforementioned cold front and shortwave will
push rain and mountain snow(above 3.5kft-4.5kft) showers east
across the forecast area, though the WA side of the Columbia Basin
is expected to remain dry. While mountain snow accumulations will
generally be 1 to 3 inches, the OR Cascade crest, interior
northern Blues, and the Wallowas are expected to see 3-5 inches of
accumulations through tonight. Otherwise, the incoming frontal
boundary and shortwave will result in breezy west winds
developing through the Cascade gaps and the Columbia Basin this
morning and persisting into the early evening. Lawhorn/82


&&

.PREV DISCUSSION... /issued 426 AM PDT Mon Mar 25 2024/

AVIATION...12Z TAFs...Mostly VFR conditions at area terminals. A
few sites will see brief MVFR conditions as moisture spreads
across the region this afternoon. There is a low chance (10-20%)
for showers at KDLS, KALW, and KPDT mainly after 21z today. VCSH
included at those terminals for any nearby showers this afternoon.
A passing disturbance will bring periods increased wind this
afternoon, with winds of 8 to 12 kts across the terminals.
Currently, KPDT is in the area with the stronger gusts with speeds
reaching up to 20 kts at points through the TAF period. Branham/76

PREV DISCUSSION... /issued 236 AM PDT Mon Mar 25 2024/

SHORT TERM...Today through Wednesday...A few weak returns noted
on the radar this morning, mainly impacting the Blue Mountains. An
approaching disturbance will advance towards the forecast area
this morning, pushing moisture and additional showers across
Oregon and Washington Cascades, as well as the Blue Mountains and
areas southeast. Current analysis shows a 25% to 45% chance for
showers over these areas this morning. As the wave pushes further
east this afternoon, shower coverage will increase. Much of the
area will see a slight to moderate chance (30-60%) for showers
through the evening hours. The exception will be around the Yakima
Valley where probabilities are around 10-15%. Gusty winds are
anticipated across the Columbia Basin, with 15 to 20 mph wind
through the evening hours.

The wave will move east of the forecast area by Tuesday morning
allowing a drier northwest flow to gain influence. Though flow
will be drier, the higher terrain and areas of eastern Oregon are
susceptible to additional showers. Through Tuesday afternoon, the
impacted higher terrain will see a 50-80% chance for showers, with
the impacted lowland areas looking at around 20-40%. With snow
levels around 3500 ft, the higher terrain will see snow, with
general accumulations of 1-3 inches, and isolated areas seeing as
much as 5 inches through Tuesday afternoon. Winds across the area
will increase, with the strongest wind favored still over the
Columbia Basin and into the Kittitas Valley where winds of 20 to
30 mph will be possible with stronger gusts.

Brief ridging will produce a break in moisture overnight Tuesday,
with the next slug of moisture advancing into the PacNW by
Wednesday morning. Confidence in precipitation related to the next
system is much higher, with showers spreading across the forecast
area through Wednesday afternoon. Much of the forecast area will
see a high chance (75-100%) for activity through Wednesday, with
the highest probabilities noted over the Cascades and the western
third of the forecast area. Snow levels will rise to around 5000
ft during this later system, with rain becoming more prevalent,
with some rain/snow mix over the higher terrain. Progression of
this system remains a bit unclear through Wednesday night as
numerical guidance continues to come into alignment on the path
and intensity. Regardless of this, models continue to agree on
some active weather during the later portion of the forecast
period. Central Oregon can anticipate some gusty winds with the
influence of this system by Wednesday afternoon. Areas of 20 to 30
mph winds are noted across the John Day Highlands and across
Deschutes County, with 10 to 20 mph winds noted across the Blues
as well.

Temperatures will generally warm through the period, with values
increasing to only a few degrees below normal by Wednesday.
However, areas of the Columbia Basin will see slight cooling on
Wednesday due to the path of the upcoming system. Branham/76

LONG TERM...Thursday through Monday..Thursday morning through
Sunday morning, an upper-level low off Oregon coast continues
pushing a frontal boundary with additional precipitation over
PacNW as it moves southerly towards the California coastline.
Consequently, this will allow more rain/snow in the low elevations
and mountain areas. By Sunday night, dry conditions will occur
when the ridge passes over the forecast area. For Friday night,
there is a difference on the position of the closed low being
slightly off Oregon coast from the cluster analysis whereas the
models has it off the California coastline (30-40% confidence).
ECWMF and GFS show wet conditions but timing seems to be off with
the occurrence of dry conditions for Saturday. Nonetheless, the
ensemble means and deterministic models seems to be good agreement
with the depth of the trough and occurrence of the oncoming ridge
Sunday night.

However, confidence is on the low side due to difference in location
of the closed low near California coastline for Friday night,
including the timing of dry conditions (30%). Temperatures will be
above normal around high 40s to 60s in the low elevations and high
20s to low 40s in the mountain areas, according to the NBM. There is
a high chance of the QPF reaching between 0.01-0.30 inches Thursday
into Friday night while the low travel southerly with precipitation
lingering in PacNW until everything dries out starting Saturday
night once near California (>70%). Snow levels will be upwards to
3000-4000ft by Thursday morning through Sunday morning along the
mountain areas while precipitation lingers as the closed low moves
near CA. As the ridge moves over the PacNW Sunday night, snow levels
will increase up to about 6000ft. Feaster/97

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  53  36  55  35 /  20  40  30  10
ALW  55  38  57  37 /  20  50  40  10
PSC  60  40  62  39 /  10  10  10  10
YKM  58  34  60  35 /  20  10   0  10
HRI  58  38  60  37 /  10  20  10  10
ELN  54  32  55  34 /  20  10  10  10
RDM  51  30  52  35 /  20  40  10  10
LGD  49  33  49  30 /  40  50  40  10
GCD  49  32  49  31 /  30  60  40  10
DLS  57  40  58  42 /  30  30  10  30

&&

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

$$

MORNING UPDATE...82
SHORT TERM...76
LONG TERM....97
AVIATION...76


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