Area Forecast Discussion
Issued by NWS Pendleton, OR

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899
FXUS66 KPDT 190342
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
743 PM PST Sun Feb 18 2018

.UPDATE...An arctic front has been sinking southward across the
forecast area through northern Oregon and southeast Washington this
evening. There has been a period of light to moderate snow across
the Lower Columbia Basin and the Blue Mountains/Foothills as well as
north central Oregon and along the Cascade east slopes. The snow is
beginning to taper off from the Blue Mountain Foothills northward
but continues to fall over the Blues due to upslope northerly winds.
Expect a gradual decrease in areal coverage and intensity of snow
overnight. May be able to cancel the Winter Weather Advisory early
for the Foothills a little later this evening but will keep the
advisory going elsewhere. Will wait another hour or two to see what
the trends are before making that decision final. A dry and cold
northerly flow will prevail over the forecast area Monday and
Tuesday with dry conditions. It will be especially cold Monday night
under mostly clear skies and light winds which will allow for good
radiational cooling. Weather systems moving into the region later
this week may bring more snow or a mixture of precipitation until
the atmosphere warms up enough for just rain by the end of the week.
Will update the forecast later this evening for any changes made to
the winter weather highlights and pops/weather. 88

&&

.AVIATION...06Z TAFs...MVFR/IFR conditions will prevail until at
least midnight from the Blue Mountain Foothills southward.
Elsewhere, north of there, it will become mostly VFR shortly under a
drying but cold northerly flow. Winds will be out of the north to
northeast mainly between 5 to 15 kts through the night. 88

&&

.PREV DISCUSSION... /issued 500 PM PST Sun Feb 18 2018/

SHORT TERM...Tonight through Wednesday...An upper level trough
continues over the region this afternoon with scattered to numerous
rain and snow showers occurring with some reports of small pea sized
hail. Also seeing the surface wind northerly flow pushing south
through Washington and now moving into northern Oregon. When this
flow begins to move into the higher terrain of Oregon we will begin
to see some enhanced upslope flow take place overnight leading to
some accumulating snowfall in some areas that have not seen much
snowfall since end of December. So, winter weather advisories have
been issued for the overnight period through early Monday. The upper
level trough will shift eastward Monday and be centered over the
northern Rockies. This will place the Pacific Northwest under the
cold dry northerly flow on the backside of the Monday through
Wednesday. Temperatures will be very cold during this period running
10 to 20 degrees below normal. Snow showers will taper off on Monday
and then remain dry through Wednesday.

LONG TERM...Wednesday night through Sunday...Northerly flow at
mid/upper levels over British Columbia through Saturday night.
This will allow a modified arctic airmass to move into the forecast
area through Saturday night for a chance of mountain Thursday
through Saturday.

Wednesday night and Thursday the models bring a weather system
dropping south from British Columbia through the region for a chance
of mountain snow with the Columbia BAsin and adjacent valleys
remaining dry. Thursday night a brief ridge of high pressure moves
across the region for dry conditions. This will be followed by a
shortwave late Friday and Saturday for snow above 1500 feet and a
mix of rain/snow in the Lower columbia Basin through Saturday
afternoon. A much stronger mid/upper level low moves out of the Gulf
of Alaska into the Pacific Northwest on Sunday for a chance of rain
and snow in the lower Columbia Basin as well as the Kittitas and
Yakima Valleys and snow at higher elevations Sunday through Sunday
night. Polan

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  22  26  11  30 /  60  20   0   0
ALW  21  25  12  31 /  60  20   0   0
PSC  22  31  14  34 /  30   0   0   0
YKM  22  30  13  32 /  20   0  10  10
HRI  22  31  13  34 /  40  10   0  10
ELN  18  28  11  28 /  20   0   0  10
RDM  18  25   4  31 /  60  20   0   0
LGD  16  17   4  24 /  60  30  10  10
GCD  17  19   4  25 /  70  30  10   0
DLS  25  33  16  35 /  60  10   0  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 9 AM PST Monday for ORZ502-503-505-
     507>511.

WA...Winter Weather Advisory until 9 AM PST Monday for WAZ030.

&&

$$

88/99/88



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