Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 252331 AAA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
335 PM PST Sun Feb 25 2018

Updated Aviation Discussion

.SHORT TERM...Tonight through Tuesday...The latest system continues
to move southeast across the Pacific Northwest this afternoon. The
system`s cold front has moved through much of the area, currently
running from north of John Day to just south of Sunriver. This front
will be out of our area before sunset. The upper level trough axis
will move through the region tonight. This trough axis, plus upslope
low level flow, will cause decent amounts of precip over the Blue
mountains east to Wallowa county, and south to central and east-
central Oregon this evening. Have a number of winter weather
advisories for snow out and will continue these highlights. Winds
have been running around 30-35 mph sustained over portions of the
lower Basin and foothills in Washington. Thus issued a wind advisory
into early evening. These winds may decrease around sunset though.
Elsewhere have been seeing bursts of wind with the passage of the
cold front. The upslope flow will keep some light snow going over
the higher terrain overnight into Monday morning. Cold air aloft and
lingering moisture will lead to a few snow showers, mainly over the
mountains Monday afternoon. Expect these showers to dissipate with
sunset Monday, leading to a mostly dry and cold night Monday night.
Some light precip from the next system may reach the Washington
Cascade east slopes late in the Monday night period. This next
system looks to be weak with most precip Tuesday confined to the
higher terrain. Temps will remain below seasonal through this
period. 90

.LONG TERM...Tuesday night through Sunday...Winter weather will
continue to affect most of the forecast area during the extended
period. Interesting that snow levels will occasionally be down to
the lowest elevations as we approach March when we receive 11 hours
of sunlight. The forecast area will be under a northwest flow aloft
Tuesday night with scattered mountain snow showers and little to no
snow elsewhere. A warm front late Wednesday into Thursday will
increase snow levels to around 2500-3500 feet and widespread
precipitation is expected during this time. Models are slower with
the timing of the warm front, and the upcoming forecast will reflect
precipitation increasing late Wednesday rather than earlier in the
day. Winds will increase Wednesday night and could be very windy in
some areas, especially in the Grande Ronde Valley. A cold front will
follow on Thursday. A deep and broad upper level trough will develop
off the eastern Pacific and the Pacific NW Thursday through Friday
night. The air mass will be moist and unstable with scattered to
numerous snow showers (rain/snow at the lowest elevations).
Afternoon temperatures will be in the mid 20s to mid 30s over the
mountains/valleys and in the mid 30s to mid 40s for areas in and
around the Columbia Basin. These temperatures are about 10-15
degrees below seasonal average. Instability will be present during
this time, and some of the snow showers could be locally heavy.  The
upper low will weaken into an open trough and travel across WA/OR
late Saturday followed by a westerly flow aloft Sunday. The ECMWF
attempts to bring another low offshore on Sunday that is not
advertised by the GFS. For now, will compromise with 20-30 percent
chance of snow and low elevation rain/snow mix for Day 7. Wister

&&

.AVIATION...00Z TAFs...The passage of a cold front has caused
aviation forecast challenges, particularly the wind direction and
speed at several TAF sites.  Winds have once again been gusty and
erratic ahead and behind the front. As stated in the short term
discussion, the front will be exiting the region by sunset. Winds
will primarily be W-NW behind the front and gradually decreasing
this evening. After midnight, winds will be variable 5-15 knots and
relatively light on Monday. Precipitation associated with the front
will lower CIGS to MVFR or less this evening...IFR/LIFR at KRDM and
KBDN as rain/snow changes to all snow in the next couple of hours.
Conditions will improve on Monday with SCT-BKN clouds with bases AOA
5000 ft AGL.  Wister

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  27  40  23  42 /  40  10   0  20
ALW  31  42  27  43 /  40  10   0  20
PSC  28  46  27  46 /  20  10   0  10
YKM  22  45  24  47 /  20  10   0  10
HRI  27  45  26  45 /  20  10   0  10
ELN  21  42  24  45 /  20  10  10  20
RDM  16  36   8  39 /  80  20  10  10
LGD  21  34  15  35 /  80  20  10  30
GCD  23  34  13  35 /  80  20  10  20
DLS  29  46  28  46 /  60  10  10  20

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 1 AM PST Monday for ORZ049-050-502-
     503-506-509.

     Winter Weather Advisory until 10 PM PST this evening for ORZ505-
     508-510-511.

WA...Winter Weather Advisory until 1 AM PST Monday for WAZ030.

     Wind Advisory until 7 PM PST this evening for WAZ028-029.

     Winter Weather Advisory until 10 PM PST this evening for WAZ520.

&&

$$

90/85/85


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