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


Updated aviation discussion 


Short term...tonight through Thursday...an 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... 
or...none. 
Washington...Wind Advisory from 11 am to 9 PM PDT Tuesday waz026. 


&& 


For additional weather information, check our web site at... 
www.Weather.Gov/Pendleton 


$$ 


90/83/83 



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