Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 160559 AAB

Area Forecast Discussion
National Weather Service Pendleton OR
955 PM PST Fri Dec 15 2017

updated the aviation discussion

.UPDATE...A disturbance was pushing through the region with
showers mainly over the far eastern cwa from the blue mountains
eastward and will be confined to these areas overnight. Elsewhere
dry conditions were moving into the region and some patchy fog
could develop in good radiational cooling over portions of the
basin and surrounding areas. Otherwise overnight temps are
expected to fall into the 20s and teens in the higher elevations
and the present short term forecast appears on track.

.AVIATION...mvfr and lcl ifr conditions can be expected at
taf site kalw. Meanwhile with the passage of the storm system
ceilings have increased some but still areas of mvfr conditions
along with lcl ifr remain at all taf sites into Saturday and these
conditions will persist into Saturday night.


.PREV DISCUSSION... /issued 521 PM PST Fri Dec 15 2017/

UPDATE...The latest radar was showing the pcpn from earlier
pushing east with drier conditions moving into the region from
the west. Thus the winter weather advisory was cancelled and the
forecast updated to remove this. No other changes expected at this

PREV DISCUSSION... /issued 325 PM PST Fri Dec 15 2017/

SHORT TERM...Tonight and Saturday...The latest Pacific cold front
continues to move across the area late this afternoon. The front and
main precip band currently runs from near Spokane south-southwest to
the Blue mountain foothills, then to central Oregon. A mix of
freezing rain, snow and sleet has been accompanying this front. The
precip has largely ended over the Lower Columbia Basin zones, and
have cancelled the winter weather advisory for those zones. Will
continue the winter weather advisory for the eastern Blue mountain
foothills zones until 7 PM, though these advisories may be eligible
for lowering prior to that time. Snow levels have been rising
slightly behind the front, but cold air advection should increase
this evening to lower the snow levels to near the Basin floor
overnight. This cold air advection, plus increasing winds and
mixing, should eliminate the remaining weakened inversions over the
area. Flow into the interior mountains will keep some showers going
through the night into Saturday morning over these mountains and
along adjacent foothills. Also should see showers continue along and
near the Cascade crest tonight and Saturday. 90

Saturday night through Sunday...A series of weak waves will move
through an offshore upper level ridge Saturday night and Sunday.
This will weaken the ridge with time. These waves will keep mostly
cloudy skies with rain and snow along the Cascades Saturday night
and Sunday. Light snow may develop in the northeast OR mountains
Sunday. Coonfield

LONG TERM...Sunday night through Wednesday night...A broad dirty
upper level ridge will slowly move across WA and OR Sunday night
through Tuesday. The series of weak waves will continue to flow over
the ridge with varying amounts of rain and mountain snow. Rain
shadowing will limit precipitation to light rain at most in the
Lower Columbia Basin, Yakima Valley, and Kittitas Valley. A rain
snow mix is possible in North Central OR and Central OR during this
time. Tuesday night an upper trough will move from the Gulf Of
Alaska to the WA and OR coast. This will bring cooler air with a
better chance of rain and mountain snow Tuesday night through
Wednesday night.  Coonfield

Thursday through Friday...ECMWF/GFS/Canadian models coming into
better agreement with mid/upper level ridging building across the
eastern Pacific, and a trough digging across the Four
Corners/Rockies region. Dry conditions can be expected area wide
with generally light winds as surface high pressure will reside
nearly overhead. There are still some model differences, but the
trend is to produce more of a northerly flow, versus a NE flow
regime previously depicted. A cooldown is still expected, but the
most frigid air will remain east of the area. Expect high
temperatures in the 30s for the lower elevations, with upper teens
to mid 20s for lows. 80


PDT  29  39  31  42 /  50  20   0  10
ALW  31  41  33  43 /  60  20   0  20
PSC  30  42  33  41 /  10  10   0  10
YKM  25  41  28  39 /   0   0  10  20
HRI  29  41  32  42 /  10  10   0  10
ELN  25  39  29  37 /  10  10  10  30
RDM  22  38  24  44 /  20  10  10  10
LGD  29  35  25  38 /  60  20   0  20
GCD  28  37  25  39 /  50  20   0  20
DLS  33  45  36  43 /  10  10  20  20




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