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Area forecast discussion...update 
National Weather Service Pendleton or
417 am PDT Monday Sep 22 2014

Updated aviation discussion

Short term...today through Wednesday night...an upper level trough
over the eastern Pacific will gradually deepen and shift east
through this period. This will keep the Pacific northwest under
south to southwest flow through the period. Moisture rotating around
a cutoff low in Idaho may trigger a few showers from Grant to
Wallowa County this morning. A weak wave moving along the Cascades
may trigger a few showers there today. Difluent flow behind the
cutoff low and daytime heating will increase the instability over
central to northeast Oregon this afternoon. Thunderstorms may
develop along the Cascades and from central to northeast Oregon and
the northern blues in Washington this afternoon and evening. A cold
front will move into the Cascades this evening and stall over the
mountains. This will start rain that will persist through Wednesday
night. While most of the cooler air will remain west of the Cascades
the upper level instability will move east and will trigger some
showers over the mountains during the night. A few showers may
linger Tuesday morning in the Blue Mountains and Wallowa and Union
counties. Tuesday night a wave will move north along the front over
the Cascades and enhance the frontal lift. This front will move
slowly east Wednesday and Wednesday night. The runoff from the
persistent rainfall in the Cascades will collect in the small
streams and will need to be monitored. Coonfield

Long term...Thursday through Monday night...uncertainty remains in
the extended forecast...with continued differences in the medium
range models. A longwave trough with associated cold front is
prognosticated to slowly move east across the region Thursday evening with
a widespread chance of showers. A slight chance of embedded
afternoon thunderstorms are also possible favoring the central and
northeast Oregon as lapse rates steepen over those regions. A
chance of showers continues overnight Thursday into Friday with a
slight chance in the Columbia Basin as the shortwave impulse
embedded within the longwave trough moves east of the area.
Significant uncertainty crops up in the weekend forecast as the
European model (ecmwf) continues to advertise a closed low over California Saturday
and Sunday that ejects northeastward across the area next Monday.
Meanwhile...the GFS suggests that the trough will continue its
eastward progression this weekend placing US under a ridge by Sunday
evening. Ensemble spreads between the GFS and European model (ecmwf) remains
significant...much like the earlier run. Have opted to continue
with the compromise from the prior forecast and coordinate minor
changes with neighboring offices until a much more clear cut
solution presents itself. Temperatures during the forecast period
will near to slightly above normal for this time of year across
southern Washington and the lower Columbia Basin of Oregon and near
to slightly below normal over central and the higher elevations of
northeast Oregon. Bieda

&&

Aviation...12z tafs. Passing upper low bringing scattered ceiling 15k feet above ground level
through 22/17z. Morning and afternoon cumulus and altocumulus buildups
with ceiling at or above 10k feet above ground level between 22/17z and 23/04z with possible isolated
thunderstorms near kbdn...krdm...kpdt and kalw. Vicinity showers
may continue after 23/04z near kpdt and kalw due to upslope flow while
all taf sites may have scattered-broken ceiling at or above 6k feet above ground level due to a passing
weather system. Winds will generally be at or below 10 kts for taf
sites...except at kdls where winds may be between 10 to 20 kts through
23/04z. Bieda

&&

Preliminary point temps/pops...
PDT 85 60 81 55 / 10 20 10 10
alw 86 64 83 60 / 10 20 10 10
psc 90 62 84 57 / 10 10 10 10
ykm 87 58 81 57 / 10 10 10 20
hri 87 57 84 53 / 10 10 10 10
eln 86 58 79 56 / 10 10 10 20
rdm 83 51 78 49 / 20 20 10 10
lgd 84 56 82 48 / 20 30 20 10
gcd 85 53 83 50 / 20 30 10 10
dls 85 56 80 56 / 10 10 10 20

&&

PDT watches/warnings/advisories...
or...none.
Washington...none.
&&

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

$$

76/98/98

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