Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 190443
AFDPDT

Area Forecast Discussion...Corrected
National Weather Service Pendleton OR
845 PM PST Wed Jan 18 2017

.UPDATE...Several forecasting challenges have been faced with the
current upper level trough over the Pacific NW.  The biggest
challenge has been the cold air that remains trapped from the East
Slopes of the WA Cascades and across the Columbia Basin and the
Eastern Columbia River Gorge.  Warm air has finally arrived to the
Oregon side of the Lower Columbia Basin where temperatures have
suddenly risen into the mid 30s to lower 40s once the wind shifted
to the East-Southeast.  The Washington side of the Basin is also
observing gradual warming over the past hour with temperatures
around 30-35.  There is a band of precipitation extending from
Wenatchee southeast to La Grande that is currently bringing freezing
rain in the Tri-Cities but this should be short-lived as
temperatures warm and the band lifts northeast in the next couple of
hours.  Observations and virtual soundings in the Kittitas and
Yakima Valleys would indicate the depth of the cold air is less than
2000 feet at this time.  The hourly temperature forecast tonight
will soon be updated to reflect the slow warming taking place in
these areas.  The Ice Storm Warning in effect for the East Slopes of
the WA Cascades...the Kittitas and Yakima Valleys...and the Eastern
Columbia River Gorge looks good but could be removed or downgraded
to a Winter Wx Advisory if the cold air is scoured out.

The current Wind Advisory for the Grande Ronde Valley and the Oregon
Blue Mtn Foothills looks on track.  The current pressure gradient
from Ontario-Meacham is about 10mb which is quite strong but not as
strong as earlier today. Gradients will continue to relax overnight.

The Winter Storm Warnings for the eastern mountains will remain in
effect although the biggest threat appears to be the sleet and
freezing rain...but several inches of new snow are possible tonight.
Wister

&&

.PREV DISCUSSION... /issued 307 PM PST Wed Jan 18 2017/

SHORT TERM....Tonight through Saturday...For Thursday...a
weakening trough will cross the area. Will keep PoPs likely for
the eastern mtns with a few inches of accumulation possible. Other
areas will experience much less precip coverage than the past few
days...with the lowest elevations mainly dry. Temperatures will be
close to seasonal norms for all areas as the coldest air gets
scoured out. The next through will approach the WA/OR coast Friday
then get stretched out across the Pacific Northwest Saturday.
Expect the greatest coverage of precip across Central OR and the
east slopes of the Cascades where high end chance to likely PoPs
will be used. Will use slight chance to low end chance further
east. Temperatures will cool to slightly below normal...with snow
levels falling from 3500-4500 feet Thursday to 1500-3000 feet
Saturday.

LONG TERM....Saturday Night Through Wednesday...An active
weather pattern will continue through Monday. Multiple disturbances
will rotate around an offshore low into eastern WA and OR Saturday
through Monday. This will keep a chance of rain and snow over the
area. Snow levels will range between 1000 and 2500 feet Saturday and
Sunday, then drop Monday as the low moves inland. Dry northerly flow
will begin Monday night with decreasing pops. A few showers may
linger over the mountains Tuesday. An upper level ridge will develop
offshore that will keep WA and OR dry Wednesday. Patchy freezing fog
may develop near the rivers early Tuesday and increase in coverage
Wednesday morning.

AVIATION...0z tafs...Mixture of VFR/MVFR this evening but brief
IFR possible near KDLS and KYKM. Expect another round of
precipitation that will bring -FZRA to KDLS. Expect BR to develop
near KYKM and possible near KRDM and KBDN. 76

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  37  44  27  38 /  60  40  20  20
ALW  36  46  31  40 /  60  40  10  20
PSC  33  41  24  36 /  50  30  10  20
YKM  32  40  22  36 /  60  20  20  50
HRI  30  40  25  36 /  50  30  10  30
ELN  28  38  22  34 /  60  30  30  50
RDM  35  40  22  37 /  30  20  10  40
LGD  33  37  26  34 /  60  60  10  30
GCD  32  40  25  36 /  60  40  10  40
DLS  32  41  32  37 /  70  30  20  50

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Ice Storm Warning until 6 AM PST Thursday for ORZ041.

     Winter Storm Warning until noon PST Thursday for ORZ050-502-503.

     Winter Storm Warning until 6 AM PST Thursday for ORZ506.

     Wind Advisory until 10 PM PST this evening for ORZ507.

     Wind Advisory until 4 AM PST Thursday for ORZ049.

     Blizzard Warning until noon PST Thursday for ORZ049.

WA...Ice Storm Warning until 6 AM PST Thursday for WAZ024-520.

     Winter Storm Warning until noon PST Thursday for WAZ030.

     Ice Storm Warning until midnight PST tonight for WAZ026-027-521.

&&

$$

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