Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 260536
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
937 PM PST Sat Feb 25 2017

Updated aviation discussion

.SHORT TERM...Tonight through Sunday night...A brief upper level
ridge over the region today is giving way to a weather system
dropping south from western Canada. Will see some increasing and
lowering clouds overnight along with an increasing chance of snow
late tonight continuing through Sunday night. Snow levels Sunday
afternoon will be between 500 and 1500 feet so precipitation will be
an occasional mix of rain and snow in the lowest elevations.
Sunday accumulations in the lowest elevations will be around an inch
while the higher elevations such as the mountains could see 2 to 4
inches. Similar snow amounts are expected Sunday night.

.AVIATION...06z TAFs. VFR conditions will prevail at all TAF sites
through early Sunday before lowering clouds and snow showers bring
about MVFR conditions through the day and into the overnight. Winds
will be less than 10 knots through the period.

&&

.PREV DISCUSSION... /issued 330 PM PST Sat Feb 25 2017/

SHORT TERM...tonight through Monday night. Upper ridge over the
area today with partly cloudy skies. Satellite shows upper low
moving south through British Columbia. This system will move into
the Pacific northwest tonight with increasing clouds and light
snow developing. Airmass fairly cold and dry tonight so expect
precipitation to start out as snow for all elevations. The snow
will continue Sunday with the upper low centered along the coast.
Gradual warming of the low levels may change the precip over to
rain or mixed rain and snow by afternoon for the Columbia basin
and some valleys. Higher elevations will remain snow as freezing
levels are about 2-3k feet. The low moves across the forecast area
Sunday night and snow is expected as temperatures fall back into
the 20s. A cold northwest flow over the region Monday associated
with the upper level trough. A short wave will be moving through
the area. Expect snow will continue through the day and into the
evening especially over the Cascades and northeast Oregon mountains.
By Mon night the trough axis is moving off to the east and
precipitation should start to diminish. Snow will linger over the
northeast Oregon mountains longest with the northwest upslope
flow. Advisories for heavy snow have been issued starting later
tonight and going into Monday night for the mountain zones where
5-10 inches accumulation is expected. 94

LONG TERM...Tuesday through Saturday.  A shortwave trough will exit
out of the region and into Idaho early Tuesday morning...leaving the
forecast area under a northwest flow aloft.  Drier air will
gradually spread from the north with showers tapering off across
most of eastern Washington Tuesday then south across eastern Oregon
Tuesday night. A flat ridge Wednesday-Thursday will keep most of the
area dry...but there will remain orographic snow showers along the
Washington and northern Oregon Cascades, the Blue Mtns, and the
Wallowas.  On Thursday...the flow will become westerly with
increasing winds aloft.  The polar jet will dive south between 40N-
50N on Friday. The ECMWF brings a 140+kt jet streak right along the
WA/OR border late Friday with a good possibility of a high wind
event east of the Cascades when strong winds aloft combine with a
tightening SW-NE surface pressure gradient.  The GFS...on the other
hand...digs the polar jet south along the Eastern Pacific then over
southern Oregon Friday night and Saturday.  If the GFS
verifies...the strong winds may not occur until Saturday and snow
levels will be quite a bit lower than the ECMWF...although
precipitation will mainly be confined to the Cascades and the
eastern mountains. Temperatures during the extended will be near to
below seasonal average with lows mainly in the mid 20s to mid 30s
and highs in the upper 30s to around 50. Wister



&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  29  37  25  38 /  20  80  70  40
ALW  30  38  26  39 /  30  80  70  50
PSC  30  40  25  41 /  20  60  60  30
YKM  26  37  21  39 /  30  60  60  30
HRI  29  40  25  41 /  20  60  60  30
ELN  25  33  17  34 /  40  70  60  40
RDM  24  36  20  38 /  10  60  50  40
LGD  25  32  22  36 /  30  70  70  60
GCD  20  31  17  35 /  10  70  60  60
DLS  30  40  25  41 /  20  60  70  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 4 AM Sunday to 4 AM PST Tuesday for
     ORZ049-050-502-503.

     Winter Weather Advisory from 1 AM Sunday to 10 PM PST Monday for
     ORZ509.

WA...Winter Weather Advisory from 4 AM Sunday to 4 AM PST Tuesday for
     WAZ030.

     Winter Weather Advisory from 1 AM Sunday to 10 PM PST Monday for
     WAZ520.

&&

$$

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