Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 050558 AAA
AFDPDT

Area Forecast Discussion...Update
National Weather Service Pendleton OR
958 PM PST Sun Dec 4 2016

Updated Aviation Discussion

.UPDATE...Frontal boundary and associated moisture is now exiting
the forecast area to the south. Scattered to broken clouds remain
over the forecast area with just isolated snow showers over the Blue
Mountains and along the East Slopes of the Cascades. Have cancelled
all headlines this evening with the snow tapering to just isolated
showers and winds decreasing below advisory criteria in all areas.
Any additional snow accumulation through the overnight will be under
1 inch. Temperatures are much cooler this evening...in the 20s to
mid 30s areawide. Overnight lows will dip into the mid and upper 20s
for most locations...except 15 to 20 in the mountains. Winds will
decrease below 10 mph for all areas by Monday morning.

The next, clipper like system is evident on the water vapor
satellite this evening along the northern BC coast. This system is
looking rather potent and will have a good deal of atmospheric
energy as it works through our area Monday afternoon...Monday night
and into Tuesday. Moisture will be limited, but snow levels will
fall below 500 feet Monday evening and to the Columbia river valley
floor Monday night. Snow ratios will be higher than 10 to 1 during
the overnight periods as well. Periods of snow and snow showers look
to overspread the forecast area from NW to SE Monday afternoon and
evening. Some rain could mix in below 500 feet before sunset. This
will likely be the first accumulating (albeit minor) snowfall of the
season for the Lower Basin, Columbia Gorge and Foothill zones. This
system may adversely affect the Monday afternoon and Tuesday morning
commutes across most of the area. Drivers should be prepared for
snow covered and slick roads during this time. Snow accumulations
Monday through Tuesday will likely range from 1 to 2 inches for much
of the area...with 2 to 4 inches in Central Oregon, Wallowa County
and most other mountain zones. This is below advisory criteria, so
will hold off on any headlines for now, but will likely issue an SPS
covering this threat. The potential does exist for higher
accumulations of snow Monday through Tuesday over the East Slopes of
the Oregon Cascades and parts of Central Oregon (near Bend,
specifically, due to an upslope flow) but confidence was not quite
high enough to issue any headlines here at this time. May need
advisories for one or both of these zones...but will let the
overnight shift decide based on the latest model data.

Otherwise temperatures will remain cold and well below average
through mid-week...with highs only in the 20s and lower 30s both
Tuesday and Wednesday. Overnight lows Tuesday night into Wednesday
morning will be down right cold...expect 10 to 18 in the lower
elevations...with -5 to 5 in the mountains and high valleys. Still
watching the potential for significant snow and/or ice accumulations
for much of the forecast area Wednesday night...Thursday and
Thursday night. With each model run confidence is growing in this
wintry scenario. 77

&&

.AVIATION...06Z TAFS...VFR conditions will persist through the
overnight period and into Monday morning. Then, the next storm
system will spread mid level clouds over the area from west to east
during the morning hours...with a mixture of light snow and rain
likely developing at KDLS and KYKM by midday. This mix of snow and
rain will move into KPSC between 05/21-24z and will then change to
all snow Monday evening. Light snow or snow showers develop at KBDN
and KRDM also between 05/21-24z. Light snow or snow showers spread
east over KPDT and KALW between 05/22 and 06/01z. This light snow or
mixture of snow and rain will bring MVFR CIGS/VIS to all terminals
Monday afternoon and evening...with tempo IFR conditions also
possible in steadier showers. The shower activity is expected to
taper off at KYKM and KDLS in the late evening, while continuing
elsewhere. Winds will generally be light and of varying
directions...under 15 KTS through the period. 77


&&

.PREV DISCUSSION... /issued 400 PM PST Sun Dec 4 2016/

SHORT TERM...Today through Tuesday night. A low pressure system and
its associated cold front raced across the two state area and was
continuing to bring clouds and showers to the area that have now
been mostly confined to the area mountains. An upslope flow will
persist into this evening along the blue/wallows mountain areas
with some additional accumulation expected. Elsewhere the showers
were decreasing while drier conditions were moving into the area.
Also pressure gradients had tightened along the foothills of the
blue mountains and a wind advisory has been issued to go along with
the advisory in the Kittitas valley.

Colder air will continue to advent into the region overnight and
another storm system will take aim on the pacnw tomorrow. This
storm will track from west to east with light snow possible
over Central Oregon in the morning and then over the Pendleton/Walla
Walla/Meacham areas Monday afternoon. Elsewhere showers will persist
into Tuesday before a weak ridge of high pressure tries to build into
our area Tuesday night. Temperatures will be noticeably colder as
overnight lows dip below freezing across most locations into
midweek.

LONG TERM...Wednesday through Sunday...Upper level ridge of high
pressure through Wednesday afternoon for dry conditions across the
Pacific Northwest. A slow moving warm front enters the forecast area
Wednesday night and spreads snow into the forecast area. The frontal
band will remain over the region on Thursday through Friday for an
extended period of snow. Snow levels will remain at the floor of the
Columbia Basin or extremely low over the Lower Columbia Basin so
snow accumulations are expected at all elevations through Friday
afternoon. Friday night a fast moving upper level shortwave moves
into the Pacific Northwest for another round of precipitation that
continues into the weekend for snow showers in the mountains and the
potential for a combinations of rain and snow showers at the lowest
elevations in the Columbia Basin during daylight hours through
Sunday.  Polan

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  27  37  21  28 /  10  50  60  30
ALW  31  38  25  30 /  10  40  60  30
PSC  29  40  26  32 /  10  50  50  20
YKM  25  37  20  33 /   0  40  40  10
HRI  28  39  26  32 /  10  50  50  20
ELN  25  34  19  30 /   0  50  40  10
RDM  21  37  19  28 /  10  50  60  50
LGD  24  34  24  28 /  20  50  50  30
GCD  22  34  23  27 /  20  50  60  30
DLS  33  40  28  35 /  10  50  30  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

77/99/77



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