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Area forecast discussion 
National Weather Service Pendleton or
450 PM PDT Monday Oct 20 2014

Updated aviation discussion

Short term...tonight through Thursday. Two upper level systems will
impact the forecast area during the short term. The first upper
level trough is offshore...and a south flow aloft ahead of the
system is preventing the trough from shifting eastward. The trough
is splitting with the strongest energy off the SW Oregon coast.
Precipitation has developed in the eastern valleys of the Cascades
and will gradually spread across the forecast area overnight. Due
to the strongest energy to the south...the southern blues and John
Day-ochoco Highlands will likely receive 0.1"-0.25" of rain
overnight. The trough will swing to the northeast as it moves into
Idaho early Tuesday morning...and similar precipitation amounts are
forecast over the northern blues and wallowas. There will be a
break between systems Tuesday and Tuesday evening before the next
upper level system moves onshore Tuesday night. This system is
currently strengthening between 140-150w over the Gulf of
Alaska...and water vapor loops clearly show a significant moisture
tap from the remains of Typhoon Vongfong. Rain will also be slow to
spread the upper level flow is parallel to the
front...and will eventually develop over all areas by Wednesday
night. A cold front with the system will lower snow levels down to
6000-6500 feet along the Cascades Thursday. 48-hour precipitation
amounts from Wednesday morning through Friday morning are around
0.25"-0.75" with the heaviest amounts in the mountains. Wister

Long term...Thursday night through Monday night...the period starts
off rather wet and unsettled across the area. Both the 20/12z European model (ecmwf)
and 20/12z GFS agree that a plume of deep...subtropical moisture
along with a strong upper level jet will be pointed at the Pacific northwest
during this period. This will lead to plenty of clouds and a good
chance for rain...or snow above 5000 to 7000 feet Thursday night
into early Friday. By late Friday into Saturday a developing upper
level low should turn the flow more southerly...perhaps leading to a
short break in the active weather. By Saturday night into Sunday the
upper level disturbance moves over the region bringing increases
chances for showers and cooler temperatures. Snow levels should also
lower to between 5000 to 6000 feet during this time. Following this
system...what appears to be a rather weak and transient upper level
ridge will try to build back into the area on Monday. High
temperatures are forecast to be right around average for this time
of year throughout the period...with low temperatures running near
to slightly above average due to the increased cloud cover/moisture.


Aviation...00z tafs...mainly VFR conditions expected at all taf
sites through the period...with some local MVFR conditions possible at
times this evening/overnight...especially at kykm..kpsc..kalw and
possibly kpdt. An upper level disturbance will move just south of
the area tonight with intermittent -shra/-ra and a broken to overcast cloud
deck between 4000-6000 feet. Westerly winds have increased at kpsc
and kpdt to 15-25 kts following the frontal passage and may also
increase some for a time this evening at kalw as the front moves
through. Winds should decrease after 21/04z at all taf sites. Then
southwest winds increase and become gusty once again after
21/18z...gusts to 15-25 kts will be possible for most locations. 77


Preliminary point temps/pops...
PDT 46 63 44 67 / 60 30 10 50
alw 50 64 48 66 / 60 30 10 40
psc 49 67 46 65 / 50 10 10 60
ykm 42 62 44 59 / 40 10 30 80
hri 47 66 44 66 / 50 20 10 60
eln 44 62 44 57 / 50 10 60 90
rdm 35 59 40 63 / 60 10 10 60
lgd 44 58 39 60 / 70 50 10 30
gcd 42 57 40 63 / 70 20 10 20
dls 47 65 47 62 / 60 20 30 80


PDT watches/warnings/advisories...

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