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Area forecast discussion...updated 
National Weather Service Pendleton or
429 PM PDT Monday Mar 30 2015

Updated aviation discussion

Short term...tonight through upper level trough will
move into the Pacific northwest late tonight and Tuesday. This
trough will push a cold front through the region between midnight
and noon Tuesday. Winds will increase with and behind this front.
Sustained winds of 20 to 30 miles per hour are expected over much of the
Columbia Basin from late Tuesday morning into the early evening.
Locations such as the Kittitas Valley and the Blue Mountain
foothills will see the strongest winds. At this time am confident
that the Kittitas Valley will see sustained winds of 30 to 35 mph,
especially over the northern side of the valley. Thus have issued a
Wind Advisory for the Kittitas Valley. Winds in the Blue Mountain
foothills may become equally strong, but confidence is lower and
will hold off on highlights for now. May see a few showers and even
a stray thunderstorm over the northern blues, the adjacent foothills
and the Grande Ronde Valley overnight ahead of the cold front. These
showers and possible storms will be caused by elevated instability.
Rain will accompany the cold front as it moves through Tuesday
morning. Cold air aloft will allow for the development of isolated
to scattered showers and a few stray thunderstorms Tuesday afternoon
and evening. Shower coverage will decrease Tuesday evening into
Wednesday morning. Also snow levels will fall Tuesday night, but
accumulations will be limited by the showery nature of the precipitation.
Cold air aloft will continue over the area Wednesday. Thus expect
isolated to scattered showers and a few stray thunderstorms to again
occur Wednesday afternoon and evening. Northwest flow will keep a
few showers going over the mountains into Thursday. 90

Long term...Thursday night through Monday...Thursday night will see
a trough departing to the east and weak temporary ridging over the
area as a front approaches out in the eastern Pacific. There will be
some lingering light snow showers in the higher mountains of eastern
Oregon and along the Washington Cascade crest. Friday will be mainly
dry with increasing clouds through the day. The front will arrive in
the late afternoon and evening with a chance of rain and snow
showers reaching as far as Yakima and Ellensburg during the day then
spreading a chance of rain and snow in the mountains and a slight
chance of rain in the lower elevations Friday night. Snow levels
will be 2500 to 3500 feet in the Cascades and 3500 to 4500 feet in
the eastern mountains. This system looks moisture deficient so
expect few hundredths of an inch of rain in most places and an inch
or less in the mountains. Friday night and Saturday an upper low
moves south out of the Gulf of Alaska and develops a trough along
the coast. Moisture moving into the area on a west to southwest flow
will keep a chance of rain and snow showers in the mountains and a
slight chance of rain in the lower elevations. Snow levels will be
back at 3000 to 4000 feet by Saturday. Models diverge with the
handling of the trough at this point with the European model (ecmwf) keeping it
offshore and expanding south through Monday. The GFS moves the
trough ashore Sunday and through the area by Monday. Both scenarios
look wet for US so have in general kept a chance of rain and snow in
the mountains and a slight chance of rain in the lower elevations.
Sunday looks unstable in the GFS so have a chance of rain in the
lower elevations for that period. If the GFS is right, would expect
some thunderstorms to develop on Sunday, but will hold off until
some better agreement is found in the models. Highs will be around
normal with highs in the middle 50s to lower 60s and middle 40s to middle 50s
in the mountains. Lows will be in the 30s and lower 40s with mainly
20s in the mountains. Perry


Aviation...00z tafs...VFR conditions will be prevalent for the next
24 hours. Ceilings early this evening will be scattered to broken
above 20k feet. After 03z middle level clouds will begin to move into
the area ahead of a cold front. Ceilings will drop to 4000-8000 feet
after 09z as light showers move through the area. Partial clearing
and an end to the showers will begin around 14z-15z. Ceilings will
be mainly scattered above 6000 feet after 20z. Winds will remain
below 12 kts through 12z tonight. After 12z winds will increase to
10-20 kts with gusts to 25 kts at all taf sites by 17z. Winds will
increase further to 15 to 25 kts with gusts to 35 kts by 21z. Perry


Preliminary point temps/pops...
PDT 44 56 35 55 / 20 50 20 30
alw 49 58 40 57 / 20 40 20 30
psc 46 63 38 62 / 10 30 10 30
ykm 42 60 34 59 / 20 20 10 30
hri 45 62 37 60 / 10 30 10 30
eln 42 56 33 55 / 20 20 10 30
rdm 37 51 24 50 / 20 40 10 40
lgd 43 53 34 51 / 20 60 20 40
gcd 39 50 29 50 / 10 50 20 30
dls 46 60 39 59 / 20 40 20 40


PDT watches/warnings/advisories...
Washington...Wind Advisory from 11 am to 9 PM PDT Tuesday waz026.


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