Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 170557
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
957 PM PST Mon Jan 16 2017

.SHORT TERM...Evening Update...The region will remain under a
weakening upper level ridge through tonight into Tuesday morning. As
such will continue to see very cold conditions across much of the
area, especially under low level inversions across the Columbia
Basin and a number of mountain valleys. Some mid/high level
cloudiness is impacting the stability at the top of the inversions,
thus low cloudiness has been struggling to redevelop over the Basin.
Still some patchy freezing fog/stratus and snow flurries will be
possible overnight into Tuesday morning. Winds have increased across
southern portions of the Grande Ronde valley and the wind advisory
in this area is on track. Precip with the next system has slowed
some and as such have slowed/lowered precip chances over the area
through Tuesday morning. Precip is also looking to be limited
Tuesday afternoon, with the main push of precip Tuesday night. 90

.LONG TERM...Previous Discussion...For Wednesday night into Thursday
morning a storm system will be impacting the area bringing periods
of rain and higher elevation snow. Snow levels are forecast to be
between 5000 to 6000 feet over Central OR...north to the Columbia
Basin and the surrounding foothills. Snow levels will be lower over
the Blue Mountains (4000-5500 feet) East Slopes of the WA
Cascades(4000-4500 feet) Grande Ronde Valley(2500-3500 feet) and
Wallowa County(3500-4200 feet). These snow levels will put the
Grande Ronde Valley...Wallowa County and parts of the Blue Mtns on
the rain/snow line. Depending on exact temperatures several inches
of snow could be possible in the Blue Mtns...Grande Ronde Valley and
Wallowa Valley through Thursday AM. There will also be some
lingering gusty south winds along the Blue Mtn Foothills and in the
Grande Ronde Valley for Wednesday night. These winds will diminish
by early Thursday morning. The forecast area will be in between
systems Thursday afternoon and the first part of Thursday night.
Chances for precipitation decrease to less than 40 percent for most
locations...and even under 15 percent in the Lower Columbia Basin
during this time. Temperatures will remain mild on Thursday...with
highs in the lower to mid 40s for the lower elevations and 30s mtns.
The next system comes in as a strong occluded frontal boundary late
Thursday night...or more likely on Friday. There remains slight
timing differences between the latest guidance on this system, with
the GFS being faster than the ECMWF by 6-12 hrs. This system will
bring additional periods of rain and higher elevation snow to much
of the area. Snow levels will be lower...between 2500-3500 feet
across the area on Friday. High temperatures will remain in the
upper 30s to lower 40s Friday afternoon in the lower elevations with
upper 20s to mid 30s in the mtns. The forecast area will continue to
see a gradual cooldown through the weekend. The Pacific NW will
remain under a broad upper level trough through the end of the long
term period. The next system looks to impact the area on Sunday and
will bring more low elevation rain and high elevation snow. Snow
levels will again slowly lower...and from this early vantage point
look to be around 2000-3000 feet. High temperatures Sunday afternoon
will be between 35-40 for the lower elevations with mid 20s to lower
30s in the mtns. Colder air and more winter like conditions look to
build into the area by early next week as an upper level ridge
begins to build offshore...putting the region under a more
northerly...continental flow of air.

&&

.AVIATION...06Z TAFS...A low level inversion remains over the
Columbia Basin, Yakima Valley and the Columbia River Gorge this
evening. This inversion looks to have a base between 2500 and 3000
ft MSL. As a result, a relatively thin stratus cloud deck has been
occurring the past few days. An area of mid level cloud is currently
moving across the region, and expect to see more areas of these
clouds move through overnight. Lift associated with these mid clouds
will continue to interfere with the development of the stratus deck.
As such have backed off on stratus and snow flurries at KDLS, KYKM,
KPSC, KALW and KPDT overnight. Increasing southeast surface flow
will keep KRDM and KBDN VFR through the night. A weak band of precip
looks to swing across the region around mid day Tuesday. Precip with
this band will be light, but should be in the form of sleet or
freezing rain across the Columbia Basin. Steadier precip will spread
across the region late in this period. All sites are expected to see
freezing rain, except KRDM and KBDN where rain is most likely. 90

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT   1  23  30  49 /  10  40  80  80
ALW   6  26  32  49 /  10  40  70  90
PSC   7  24  28  42 /  10  40  80  70
YKM  11  23  29  40 /  10  60  60  60
HRI   2  23  28  44 /  10  40  70  70
ELN   7  24  26  38 /  10  60  70  60
RDM   8  34  30  45 /  10  30  60  50
LGD  10  28  30  40 /  10  40  80  80
GCD  16  34  29  40 /   0  30  70  70
DLS  11  27  32  40 /  10  60  80  80

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Air Stagnation Advisory until 10 AM PST Tuesday for ORZ041-044-
     049-050-505-507-508-510-511.

     Winter Storm Watch from Tuesday morning through Wednesday
     morning for ORZ044-507-508-510.

     Winter Weather Advisory from 4 PM Tuesday to 10 AM PST Wednesday
     for ORZ050.

     Winter Weather Advisory from 4 PM Tuesday to 4 AM PST Wednesday
     for ORZ049.

     Wind Advisory until 4 AM PST Thursday for ORZ049.

WA...Air Stagnation Advisory until 10 AM PST Tuesday for WAZ024-
     026>029-521.

     Winter Storm Watch from Tuesday morning through Wednesday
     morning for WAZ028-029.

     Winter Weather Advisory from 4 AM Tuesday to 4 AM PST Wednesday
     for WAZ026-027.

     Winter Weather Advisory until 8 PM PST Tuesday for WAZ520.

     Winter Weather Advisory from 4 AM to 8 PM PST Tuesday for WAZ521.

&&

$$

90/77/90



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