Area Forecast Discussion
Issued by NWS Pendleton, OR

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FXUS66 KPDT 170558 AAA
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
955 PM PST Sat Dec 16 2017

updated the aviation discussion

.UPDATE...Clearing skies is allowing for good radiational cooling
and producing patchy freezing fog across the region such as in
the yakima valley and along the foothills of the blue mountains.
Thus the forecast was updated to reflect this overnight and the
surrounding locations. A disturbance will approach the region
overnight and spread mid and high level clouds to the area. A few
showers will develop mainly along the wa cascades tonight and
this will migrate south into the oregon cascades overnight before
spreading into the ykm and kittitas valleys and then the blue
mountains tomorrow morning. Minor adjustments were performed on
overnight lows especially over wallowa county where temps had fallen
more dramatically due to the clear skies and calm winds and the
present short term forecast appears more on track.

.AVIATION...areas of mvfr and lcl ifr in patchy freezing fog will
effect taf sites kykm and kalw before a disturbance moves into the
region after 08z and the fog should lessen at these locations.
Elsewhere a mixture of vfr and lcl mvfr conditions should persist
into tomorrow. The mvfr conditions should mainly develop in and
near showers that occur at or close to the taf sites.

&&

.PREV DISCUSSION... /issued 234 PM PST Sat Dec 16 2017/

SHORT TERM...Tonight through Monday...A weak upper level ridge will
be over the Pacific Northwest tonight. There will be a fair amount
of mid and high level cloudiness moving over the ridge tonight. Thus
will see partly to mostly cloudy conditions, though will see mostly
thin high clouds over central Oregon. Also will see a fair amount of
lower clouds over portions of the Columbia Basin, especially in
Washington. There will also be some patchy fog in the basin late
tonight into Sunday morning. The cloud cover will keep low temps
from getting too cold, except in central and east-central Oregon
where the clouds will be thinner. There will some light snow along
the Cascade east slope (mainly in Washington), and may see some
light precip east across the Kittitas and Yakima valleys, the Gorge
and the Simcoe Highlands. For Sunday through Monday, the region will
be under a moist west-northwest upper level flow. Thus will see
varying chances of precip over the mountains, particularly over the
Washington Cascade east slopes. Also may see occasional very light
precip amounts at the lower elevations. Snow levels will rise Sunday
afternoon into Monday, thus snow will be limited at locations below
3000 to 4000 feet. Winds will increase Sunday night into Monday
leading to gradually milder temps. 90

LONG TERM...Monday night through Saturday. Unsettled weather will
continue into the first part of the extended period. Northwest flow
will persist Monday night with a frontal boundary across Washington,
with most of the moisture over Washington. The flow will turn more
southwest on Tuesday as an upper level low pressure system will be
dropping along the west Coast of Canada. The low pressure system
will continue across the area Tuesday night with widespread
precipitation, mainly rain in the lower elevations and mountain
snow. The system will be exiting the region on Wednesday with much
colder and mainly dry northerly flow expected through the rest of
the extended period. Temperatures by late in the week will be 5 to
10 degrees below normal. 93

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  28  42  37  50 /  10  20  20  20
ALW  31  43  39  50 /  10  20  30  30
PSC  31  39  37  49 /  10  20  10  10
YKM  27  37  33  46 /  20  20  10  20
HRI  27  40  38  51 /  10  10  10  10
ELN  29  37  33  44 /  20  40  10  20
RDM  21  44  30  49 /  10  10  10  10
LGD  23  38  35  42 /   0  20  30  30
GCD  23  40  35  46 /  10  10  20  20
DLS  36  44  39  50 /  20  20  20  30

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

97/97



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