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583
FXUS66 KPDT 261010
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
310 AM PDT Sun May 26 2024

.SHORT TERM...
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Today through Tuesday Night...
The forecast area is currently under a westerly flow aloft though
an upper low and trough in the Gulf of Alaska is beginning to
sink south to the northern British Columbia coast. The flow around
the low will turn the flow over our area more to the southwest
and build a modest ridge over the area today. This will give us
fair and warmer weather today. Temperatures will be 5 to 10
degrees warmer today in the Columbia Basin and as much as 10 to 15
degrees warmer in the rest of the area. This will bring
temperatures to the lower to mid 70s in the lower elevations and
mainly in the 60s in the mountains, which is near to a couple of
degrees below normal. The only chance for light rain showers will
be along the Washington Cascade crest, perhaps reaching as far
east as Cle Elum. Pressure gradients will be much weaker today
with any winds as strong as 15-20 mph confined to the Kittitas
Valley and in the Simcoe Highlands near Goldendale.

The ridge will continue to build Sunday night into Memorial Day
as the upper low remains parked along the northern British
Columbia coast. Skies will remain mostly clear Sunday night though
the building ridge will keep temperatures up despite the chance
for radiative cooling under the mostly clear skies. Temperatures
will warm to the upper 30s and 40s and probabilistic guidance
shows a virtually zero chance of freezing temperatures away from
the highest mountains.

Memorial Day becomes more interesting as the ridge strengthens
further though the ridge axis moves into Idaho and the southwest
flow over our area strengthens. Mid level moisture increases and
with temperatures warming to the mid 70s and lower 80s, we get
increasing instability through the day with CAPE values of up to
500 J/kg and Lifted Indices reaching -1 over the mountains.
Existing forecast calls for a slight chance of eastern mountain
thunderstorms in the afternoon and early evening. Have tweaked the
timing and coverage to have a slight chance of thunderstorms over
the southern Blues and Ochoco-John Day Highlands in the early
afternoon and then into most of the eastern mountains in the late
afternoon before having them end soon after sundown. Can`t rule
out a cell or two in southern Deschutes or Crook counties (indeed,
that`s where the SPC paintball plots put 2-3 cells) but did not
have enough confidence to add them there. This is a fairly
marginal situation (and only some of the models support this), so
do not expect any of the storms to become strong, just having some
brief light showers with a handful of lightning strikes. There
could be a few showers getting into the Blue Mountain Foothills in
the late evening and overnight. Increased cloud cover will keep
temperatures up Monday night with lows in the upper 40s to mid 50s
in the Columbia Basin and in the mid to upper 40s elsewhere.

As we get into Tuesday, a short wave travels through the base of
the trough, which is now centered along the coast. The short wave
will push a cold front into the area in the afternoon and evening.
This will give us likely rain showers and a slight chance of
thunderstorms in the eastern mountains in the afternoon and early
evening. However, in the late afternoon and early evening the
thunderstorm chances will become more scattered than isolated in
eastern Wallowa County and SPC has placed a marginal chance of
severe storms there with the primary threats being gusty outflow
winds and moderate to heavy rain showers. Rain amounts will be a
quarter to a half inch in Wallowa county but locally higher
amounts will be possible. Other parts of the eastern mountains
will have one to two tenths of an inch of rain. The Washington
Cascades and the Blue Mountain Foothills will also have a slight
chance of rain showers with just a few hundredths of an inch or
less. The front will bring westerly 15 to 25 mph winds to the
Columbia Basin and adjacent valleys in the afternoon and early
evening. Highs Tuesday will drop 3 to 7 degrees to the mid 70s to
lower 80s in the Columbia Basin and mainly in the 70s elsewhere.
Lows will drop a similar amounts to the 40s and lower 50s with
some upper 30s in the mountain locations. Perry/83

.LONG TERM...
Wednesday through Saturday...An upper level trough will be
located over the Pacific Northwest at the start of the extended
period on Wednesday.  This trough will move eastward Wednesday night
and northwesterly flow will build in over the area for Thursday into
Friday.  Ridging will then move into the region for later Friday
into early Saturday, followed by a more zonal westerly flow for
Saturday.

With the trough over the area on Wednesday, there will be showers,
mainly across the mountains and the potential for afternoon/evening
thunderstorms. Additionally winds will become breezy Wednesday
afternoon into Wednesday evening, especially across the Columbia
Basin, Gorge, Foothills of the Blue Mountains, Simcoe Highlands and
Kittitas Valley.  Winds should gust in the 25 to 35 mph range, with
some gusts to 40 mph. NBM probabilities of wind gusts >= 39 mph on
Wednesday are 80 to 100% in the locations mentioned above. NBM
probabilities of wind gusts >= 47 mph are generally 30% or less
except for the Kittitas Valley where the probability is around 40%.

Dry weather is then expected by Thursday afternoon everywhere,
though most locations, outside of the mountains will be dry
Wednesday.  The remainder of the forecast is dry until later
Saturday, when some precipitation returns to the Cascades.

Deterministic models are in generally good agreement through the
period, though there is a bit more uncertainty on Saturday, mainly
involving the flow pattern and the presence or absence of a weak
trough.  However, at this time the forecast for Saturday is dry, so
any of these differences don`t have any effect on sensible weather.
The ECMWF ensemble mean does have better agreement with its
deterministic run at 500 mb leading to some more support for its
solution.

Temperatures will rise through the period from the 60s across most
of the area and lower 70s in the Basin on Wednesday...which is below
normal.  By Saturday, everyone will be in the low to mid 80s which
is a few degrees above normal.
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&&

.AVIATION...
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12Z TAFS...VFR conditions are expected through the TAF period.
DLS will see winds gust again between 20 and 25 kts.  PDT and ALW
could see afternoon winds to around 15 kts.  Everywhere else should
be 10 kts or less.
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&&

.PRELIMINARY POINT TEMPS/POPS...
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PDT  70  45  78  52 /   0   0  10  10
ALW  73  50  81  56 /   0   0   0  10
PSC  76  50  83  58 /   0  10   0   0
YKM  72  42  80  50 /  10   0   0   0
HRI  76  48  83  55 /   0  10   0  10
ELN  66  43  77  51 /  10   0   0   0
RDM  72  40  79  46 /   0   0   0  10
LGD  68  43  78  49 /  10   0  10  20
GCD  71  43  81  49 /   0   0  10  20
DLS  73  50  80  54 /   0   0   0   0
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&&

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

$$

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