Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 072323
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
323 PM PST Wed Dec 7 2016

Updated aviation discussion

.SHORT TERM...Tonight through Friday. A complex pattern will set up
over the Pacific NW through the short term period...and many
forecast challenges were encountered.  Multiple Winter Storm
Watches, Warnings and Advisories will be issued for the afternoon
package.  The Winter Storm Watches for the East Slopes of the WA
Cascades...the Eastern Columbia River Gorge and North Central Oregon
will be upgraded to Winter Storm Warnings for heavy snow and the
potential for freezing precipitation.  Snow will begin to develop
along the East Slopes of the Oregon Cascades in Deschutes County and
the Bend/Redmond areas around 5 AM Thursday.  The snow will then
spread over the remainder of eastern Oregon and eastern Washington
during  the day.  The warm front bringing the precipitation is
arriving slower than previously anticipated...and most of our
eastern Washington zones will not see snow develop until after 12 PM
Thursday.  Models have also backed off on the QPF for the area due
to a more stretched out warm front and a surface low farther west
than previous runs were advertising.  Therefore...snow amounts in
the Kittitas/Yakima Valleys...the Simcoe Highlands...the Lower
Columbia Basin and Blue Mtn Foothills will be less than the previous
forecast indicated and should only meet advisory criteria. Rather
than making a decision to downgrade the watch to an advisory...will
let the next shift analyze the system and decide the best highlights
(if any) for these areas. Forecasters will also need to consider
where freezing rain or sleet may occur due to the weak warm air
advection expected. The timing of the Winter Storm Watch will be
changed to reflect the slower moving front.

Winter Weather Advisories will be issued for the Blue Mtns...the
John Day Basin...and the Ochoco Mountains.  Snow amounts of 2-4
inches are forecast for the John Day Basin and 3-5 inches in the
Ochoco Mountains on Thursday before warm air spreads and increases
snow levels to around 3500-4000 feet.  In the Blue Mtns...light snow
will be continue from Thursday afternoon through Friday night...and
this will be a prolonged light to moderate snow event.  Snow amounts
in the Grande Ronde Valley and Wallowa County are not expected to
become significant...but windy conditions in the Grande Ronde Valley
late Thursday will cause blowing and drifting of snow.  Wister


.LONG TERM...Friday night through Wednesday...Extended models have
come into better agreement through the extended period so confidence
is better than yesterdays low confidence but still need some
consistency over the coming model runs.

A cold front will be passing over the region Friday night and snow
levels will vary due to the cold pool trapped in the Columbia Basin.
Most precipitation type will be snow but could see some wintery mix
over portions of the Basin. This will leave us in a west to
northwest flow over the weekend with small shortwaves passing over
the region. Precipitation will taper off Saturday to showers before
another system increases precipitation late Sunday and Sunday night.
A small upper level ridge will begin to build first of next week
which will begin to turn the flow more southwesterly. The new trend
in the models is to bring some warm fronts into the region tuesday
and Wednesday associated with this building ridge pattern. However,c
confidence in this solution is low at this time as models have had
issues agreeing over the past couple of days. Overall the weather
pattern looks to remain active with wintery weather impacting the
forecast area through the long term forecast period.


&&

.AVIATION...00Z TAFs...VFR conditions are expected through most
of tonight at all TAF sites. The exception will be at KRDM and KBDN
late tonight after 06Z when the next system spreads snow into
central Oregon which will create MVFR or IFR conditions at times due
to lower visibility and cigs in snow. These conditions will spread
north early Thursday eventually impacting all TAF sites. Winds will
be light and mostly 10 kts or less at all TAF sites.

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  12  27  21  35 /   0  90  80  60
ALW  16  28  26  37 /   0  80  90  60
PSC  16  27  24  32 /   0  70  80  40
YKM  14  25  18  31 /   0  90  90  40
HRI  14  26  22  32 /   0  90  80  40
ELN  12  23  19  29 /   0  60  90  40
RDM  12  30  24  40 /  20  80  50  50
LGD  12  28  25  37 /   0  90  80  70
GCD  15  33  31  39 /   0  80  70  70
DLS  22  29  24  38 /   0 100  90  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 4 AM to 10 PM PST Thursday for
     ORZ509-511.

     Winter Storm Warning from 7 AM to 10 PM PST Thursday for ORZ510.

     Winter Weather Advisory from 7 AM to 10 PM PST Thursday for
     ORZ505-506.

     Winter Weather Advisory from noon Thursday to 4 AM PST Saturday
     for ORZ502.

     Winter Storm Watch from Thursday morning through Friday evening
     for ORZ044-507-508.

     Winter Storm Warning from 10 AM to 7 PM PST Thursday for ORZ041.

WA...Winter Weather Advisory from noon Thursday to 4 AM PST Saturday
     for WAZ030.

     Winter Storm Watch from Thursday afternoon through Friday
     evening for WAZ521.

     Winter Storm Warning from noon Thursday to 3 PM PST Saturday for
     WAZ520.

     Winter Storm Warning from 10 AM to 7 PM PST Thursday for WAZ024.

     Winter Storm Watch from Thursday afternoon through Friday
     evening for WAZ026>029.

&&

$$

85/91/91



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