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fxus66 kpdt 282126 

Area forecast discussion
National Weather Service Pendleton or
226 PM PDT Fri Apr 28 2017

Short term...tonight through upper level ridge centered
offshore has expanded over the area as an upper low over The Rockies
has moved south and further away from our area. A dry north to
northwest flow is over the area and skies have been clearing this
afternoon. While the mountains will remain partly cloudy this
evening, skies will be generally mostly clear with little chance of
precipitation. Breezy winds this afternoon will die down this
evening and become light overnight. This will set up good conditions
for radiative cooling but the increasing influence of the ridge will
keep temperatures from falling too far, perhaps a couple of degrees
cooler than last night with mid to upper 30s in the lower elevations
and mid 20s to lower 30s in the mountains. Tomorrow the ridge will
move overhead by the afternoon but it will be flattening as a system
rides over the ridge. Saturday should see clouds increasing in the
afternoon. A chance of showers should hold off until the evening
along the Cascades and then over much of the area overnight and
Sunday morning though the Columbia Basin should be mainly dry. Snow
levels will be around 6000 feet so rain will be the main form of
precipitation. Rain amounts will be light with less than a tenth of
an inch in the lower elevations and up to two tenths of an inch in
the mountains. As the system clears the area Sunday afternoon,
pressure gradients will strengthen and winds will increase. Thus far
it looks like winds will be 15 to 25 mph in central Oregon, 20 to 30
mph in the Columbia Basin and 25 to 35 mph in the Columbia Gorge and
Kittitas Valley. May need to issue a Wind Advisory or two for then
but will keep evaluating for now. Sunday night and Monday, the ridge
will be rebuilding offshore and the forecast area will be dry aside
from a few showers along the Cascade crest. Monday afternoon,
another shortwave will move into the area with very light rain
showers mainly in the mountains. Snow levels will be at 4500-5500
feet. Temperatures Saturday through Monday will be in the mid to
upper 60s with 50s and lower 60s in the mountains. Lows Saturday
night will be in the mid 40s to lower 50s with mid 30s to lower 40s
in the mountains. Sunday night will cool to the upper 30s to mid 40s
with upper 20s to mid 30s in the mountains. Perry

Long term...Monday night through Wednesday night...on Monday
evening a low amplitude shortwave trough will move quickly across
the area in northwest flow aloft and may produce a few mountain rain
showers. It should be dry overnight. Tuesday through Wednesday night
a rather pronounced ridge of high pressure will build over the
western U.S. This will result in dry and warming conditions. Highs
will be around 70 lower elevations Tuesday and well into the 70s
Wednesday...with 50s/60s mountains both days. 78

Thursday morning through Saturday...there is substantial uncertainty
in the position/strength of the of the trough approaching the coast
on Thursday night. Have opted away from the operational GFS and more
toward the European model (ecmwf)/Canadian solution...which is also more in line with
the GFS ensemble mean. Instability will increase ahead of the
approaching trough as lapse rates steepen Thursday night into Friday
morning with a chance of showers and perhaps a couple of
thunderstorms especially across the eastern slopes of the Oregon
Cascades and southern Blue Mountains. On Saturday, showers will
clear the area from west to east as the trough clears the forecast
area. 74


Aviation...00z tafs...VFR conditions will prevail through the
forecast period. Few flat cumulus this afternoon will dissipate
after sunset leaving just some high clouds tonight. Winds will
decrease this evening to terrain driven at 10 kt or less overnight.
Increasing mid and high broken-overcast ceilings are expected after 18z Saturday
as the next storm system approaches. 78


Preliminary point temps/pops...
PDT 36 63 49 63 / 0 0 30 30
alw 41 65 50 66 / 0 0 40 40
psc 38 67 50 68 / 0 0 20 10
ykm 37 64 43 64 / 0 0 20 10
hri 37 65 49 66 / 0 0 20 20
eln 36 59 42 57 / 0 0 30 10
rdm 25 62 42 59 / 0 0 20 20
lgd 32 61 44 58 / 10 0 30 40
gcd 29 62 42 61 / 0 0 20 30
dls 40 64 47 61 / 0 0 30 20


PDT watches/warnings/advisories...

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