Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 171938 AAA
AFDPDT

Area Forecast Discussion...Updated
National Weather Service Pendleton OR
1135 AM PST Sat Feb 17 2018

Updated AVIATOIN discussion

.SHORT TERM...Today and tonight...An upper level trough is
approaching the region with a warm front across Washington and
northeast Oregon this morning. This will produce low elevation rain
and snow above. The trough will push a fast moving cold front
through the area late this afternoon and evening which will be
accompanied by a strong upper level jet. These winds are expected to
mix down to the surface producing some very strong winds to portions
of the forecast area up to 10pm and then winds will gradually
decrease overnight. Some of the wind advisories have been upgraded
to high wind warnings. The Blue mountains have been placed under a
high wind warning in addition to the winter storm warning. This
could result in some blizzard like conditions in the Blue Mountains
mainly above 4500 feet this afternoon and evening. Forecast has been
updated to reflect these changes.

&&

.AVIATION...18Z TAFs...A strong mid/upper level shortwave will move
east of the Cascades early this afternoon and track across SE
Washington and central and NE Oregon bringing lower elevation rain
and mountain rain and snow today through Sunday afternoon. At lower
elevations rain will taper off with rain ending by sundown today at
TAF sites. Snow will continue in the Blue Mountains through Sunday
afternoon. Cloud cover at TAF sites will be mainly broken to
overcast with cloud bases at lower end mid levels SCT-BKN 040-050
AGL thus VFR conditions expected at all TAF sites through 18Z Sunday.

Main concern is the increasing winds at all Columbia Basin TAF sites
where winds are expected to reach 25 to 35 kts with gusts to 40 to
45 kts this afternoon into early this evening. KRDM and KBDN will
reach 25 kts with gusts of 35 to 40 kts.

The aforementioned shortwave will bring a low level jet streak east
of the Cascades today resulting in very windy conditions. Winds at
850 MB (around 5000 feet above MSL) this afternoon will be 55 to 65
kts so the potential for even stronger winds will exist, but believe
that those higher winds aloft will not fully mix down to the
surface. Winds will gradually decrease after 04Z but will remain at
15 to 20 kts with gusts to 30 kts until 10Z.

LLWS is possible this afternoon. Non-convective vertical wind shear
of 10 to 15 kts is possible within 2000 feet of the airports at
KPSC, KPDT an KALW this afternoon.  Polan

&&

.PREVIOUS DISCUSSION... /issued 402 AM PST Sat Feb 17 2018/

SHORT TERM...Today through Monday. Upper level trough moving
across the Pacific northwest today. This will bring rain and
mountain snow with significant accumulations for the Cascades and
Blues. Strong winds aloft associated with this system. Will
continue with wind advisories for a good portion of the forecast
area with highest winds expected during the afternoon and evening.
Potential for winds aloft to mix down at times which would result
in higher gusts to 50 mph. Precipitation and winds will diminish
overnight although steady snow will likely continue for the
Cascades and Blues with the westerly flow aloft. Another upper
level trough and cold front will then move south across the
region Sunday. This is a much colder system and expect snow for
all locations later Sunday into Sunday night. Northerly flow
Monday with continued cold advection and snow showers over the
mountains. High temperatures today will be in the 40s and 50s
falling into the 20s and 30s Sunday and teens to 20s Monday.
94

LONG TERM...Monday Night through Saturday...A deep upper trough
will be over the area Monday night and an open wave will be
departing to the east Monday night and Tuesday. This will shift the
trough axis into Idaho by Tuesday afternoon. A few lingering snow
showers will remain in eastern Wallowa county Monday evening but
otherwise the forecast will be dry through Tuesday night. The main
story will be cold air arriving on a northerly flow aloft. This will
keep the coldest weather of the winter with us for a few days.
Monday night will see temperatures of 5 to 15 in the lower
elevations and 5 below to 5 above zero in the mountains. Tuesday
will see temperatures in the upper 20s to mid 30s with mid teens to
mid 20s in the mountains. Tuesday night will see some modest warming
as the flow turns a little to the northwest with lows of 10 to 20
and in the mountains lows of zero to 10 above. Wednesday afternoon
through Thursday models show another wave moving into the area
though they differ greatly in the details. The GFS has a fairly weak
wave staying mostly to our north while the ECMWF has a much stronger
wave that it sends right through our area with another shot of cold
air. Took a middle ground for now and have a chance of snow in the
mountains and a slight chance of mainly snow in the lower
elevations as snow levels remain close to the surface. Moisture is
limited so it does not appear that snow will be more than an inch or
two even in the mountains. Thursday night through Saturday models
are completely disagreeing with the GFS maintaining a progressive
northwesterly flow with a series of embedded disturbances. The ECMWF
has a transitory ridge over the area Thursday night and Friday
before another deep and cold low arrives Friday night and Saturday.
Have kept a chance of snow in the mountains for Thursday night
through Saturday with a slight chance of snow in the lower elevation
with some rain mixed in in the Columbia Basin. Temperatures
Wednesday and Thursday will be in the mid 30s to lower 40s with
upper 20s and 30s in the mountains. Warming will continue Friday and
Saturday with highs in the mid 40s to lower 50s in the lower
elevations and in the mid 30s to lower 40s in the mountains. Perry

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  54  36  35  15 /  90  20  60  60
ALW  53  36  36  17 /  90  20  70  60
PSC  56  37  37  19 /  80  10  60  30
YKM  54  31  36  17 /  50  10  60  30
HRI  58  37  38  18 /  80  10  60  40
ELN  47  28  31  14 /  70  20  60  30
RDM  52  28  35  12 /  20  10  50  60
LGD  43  32  34  12 / 100  80  60  60
GCD  47  31  33  11 /  40  40  60  50
DLS  55  38  40  20 /  40  20  60  60

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 10 PM PST this evening for ORZ041-044-
     502-503-507-508-510.

     Winter Storm Warning until 6 PM PST Sunday for ORZ509.

     Winter Storm Warning until 10 PM PST Sunday for ORZ502.

     Wind Advisory until 10 PM PST this evening for ORZ511.

WA...High Wind Warning until 10 PM PST this evening for WAZ024-
     028>030-521.

     Winter Storm Warning until 6 PM PST Sunday for WAZ520.

     Winter Storm Warning until 10 PM PST Sunday for WAZ030.

     Wind Advisory until 10 PM PST this evening for WAZ026-027.

&&

$$

91/99/99


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