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142
FXUS66 KPDT 250929
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
229 AM PDT Sat May 25 2024

.SHORT TERM...
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Today through Monday night...An upper trough over the Pacific
Northwest will move eastward during the day today. Some generally
light showers, mainly over the mountains will occur early before
drying commences as dry northwesterly flow moves in over the
entire region.

Dry weather is then expected for the remainder of the short term
period, with the exception of the Washington Cascades, where there
could be a few showers on Sunday.

The flow will become more westerly on Sunday then southwesterly
Sunday night. By Monday night, there could be a few showers,
mainly over the Blue Mountains. However, for the vast majority of
the area, the holiday weekend looks dry, with warming temperatures
each day.

With the trough over the Pacific Northwest today, there will be
some breezy conditions, mainly over the Oregon Columbia Basin,
Simcoe Highlands and Kittitas Valley. Winds should gust in the 25
to 35 mph range, with locally higher gusts to 40 mph possible. The
NBM probabilities of winds >= 39 mph in these locations are
70-100%. However, the wind gust probabilities of >= 47 mph are
generally 40% or less. The ECMWF EFI also keys in on wind gusts
across much of this area, with values mainly in the 0.6 to 0.7
range.

High temperatures today will be 5 to 10 degrees below normal, with
readings mainly from the low 60s to possibly the lower 70s in the
Columbia Basin. Highs on Sunday will be much warmer and much
closer to normal and generally in the low to mid 70s everywhere.
On Memorial Day, highs will be warmer still, and will be 5 to 10
degrees above normal, ranging from the upper 70s to lower 80s.


.LONG TERM...
Tuesday through Saturday...Models start out in good agreement in
having a ridge over the Rockies and a closed low and trough off
the west coast. A cold front will come ashore in the afternoon and
evening followed by a second weaker front Wednesday. Models are
diverging by Thursday with 71 percent of model ensemble members
having a trough somewhere over the Pacific Northwest while the
remaining 29 percent have a flat westerly flow over the area.
Differences grow on Friday as model ensemble members are fairly
equally divided between having a ridge overhead, a trough overhead
or a ridge offshore with a shallow trough over northern Montana
and southern Saskatchewan. Friday shows a similar widely varied
set of solutions though there is a preference of a ridge somewhere
over the region with only 20 percent of model ensemble members
favoring a trough over our area. Fortunately, the Extreme Forecast
Index shows few concerns in the long term period. It does
highlight convective energy for thunderstorms over the eastern
Oregon mountains on Tuesday with a 0.70 value. It also highlights
below normal high temperatures on Wednesday and Thursday and below
normal low temperatures Thursday morning and Friday morning with
values of
-0.67 to -0.75 mainly over the mountains. Overall forecast
confidence is good on Tuesday and then declines, becoming below
normal by Friday and Saturday.

On Tuesday, the cold front will bring a chance of showers to the
mountains and the Blue Mountain Foothills along with a chance of
thunderstorms in the eastern mountains in the afternoon and evening
before tapering off overnight. The eastern mountains will get as
much as a third of an inch of rain while other areas with
precipitation will have just a few hundredths of an inch. Winds will
pick up with the frontal passage and westerly winds of 15 to 25 mph
are anticipated in the afternoon and early evening. The front will
affect temperatures in central Oregon the most with temperatures
dropping 6 to 8 degrees to the lower 70s while the rest of the area
will cool 2 to 4 degrees to the mid 70s to lower 80s. Low
temperatures Wednesday morning will cool 4 to 8 degrees to the mid
40s to lower 50s in the Columbia Basin and in the upper 30s to mid
40s elsewhere.

On Wednesday, models favor the trough moving ashore with a weakening
closed low over British Columbia and then crossing the area though
Wednesday night. The mountains will have a chance of afternoon
showers with just minor amounts of rain. A slight chance of
thunderstorms will be confined to the higher terrain near John Day.
The afternoon will have a recurrence of westerly afternoon winds
though a little slower at 10 to 20 mph. With the low overhead,
temperatures will cool further to the 60s with a few lower 70s in
the Columbia Basin.

Thursday becomes more uncertain, but the GFS and ECMWF deterministic
runs both have the departing low and trough over western Montana
with moisture circulating into the eastern mountains and further
west, an upslope flow into the Cascades. Have kept a chance of
showers and a slight chance of thunderstorms over the eastern
mountains and a slight chance of showers elsewhere except dry in the
Columbia Basin. Rain amounts will be up to a tenth of an inch in the
mountains and light elsewhere. Temperatures will be a degree or two
cooler than Wednesday.

Uncertainty continues on Friday and Saturday though the model
deterministic runs favor a ridge crossing the area, so have a slight
chance of very light mountain rain showers Friday and Saturday.
Temperatures begin recovering to the mid 60s to mid 70s Friday and
then to the 70s on Saturday. Perry/83
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&&

.AVIATION...
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(Previous Discussion)
06Z TAFs...VFR conditions to prevail through the period. Winds
will continue to be 12-15kts with gusts 20-25kts at sites DLS/PDT
tonight, then increasing to 20-25kts with gusts 30-35kts by late
tomorrow morning. All other sites will see light winds, 12kts or
less, then increasing to 12-20kts with gusts 20-25kts
tomorrow...except site BDN where winds are expected to be 12kts or
less tomorrow. Lawhorn/82
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&&

.PRELIMINARY POINT TEMPS/POPS...
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PDT  62  40  70  46 /   0   0   0   0
ALW  66  45  73  49 /  10   0   0   0
PSC  71  46  76  51 /   0   0   0   0
YKM  68  40  72  44 /   0   0   0   0
HRI  67  44  76  49 /   0   0   0   0
ELN  62  43  66  44 /   0  10   0   0
RDM  59  33  71  41 /   0   0   0   0
LGD  59  36  68  42 /  30   0   0   0
GCD  59  35  70  43 /  30   0   0   0
DLS  64  45  73  49 /   0   0   0   0
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&&

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

$$

SHORT TERM...77
LONG TERM....83
AVIATION...83