277 
FXUS66 KPDT 170421
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
821 PM PST Mon Dec 16 2019

.UPDATE...Satellite currently showing some high clouds passing
over the region tonight, with a much lower deck covering much of
the Lower Columbia Basin, and portions of the Foothills of the 
Blue mountains in OR and WA. Observations also show that places 
along the central WA and OR border are under dense freezing fog, 
with visibilities at one quarter of a mile. For overnight, have 
included the foothills of the Blue Mountains in OR to the dense 
freezing fog advisory, which is still in effect for the Oregon 
Lower Columbia Basin, foothills of the Blue Mountains, and the 
Yakima and Kittitas valleys. Have adjusted winds slightly in the 
Grande Ronde valley and the rest of the forecast area for the 
short term, though no change to the wind advisory. Expect some
areas of the Lower Columbia Basin to fill in with freezing fog
overnight, and current regions to see fog persist to the morning
hours. Central OR is currently under thin cirrus, and should
expect mostly clear skies overnight. Otherwise, rest of forecast 
on track for the overnight hours. Lawhorn

&&

.PREV DISCUSSION... /issued 223 PM PST Mon Dec 16 2019/ 

SHORT TERM...Tonight through Thursday...Center of an upper ridge
will move overhead tonight then shift eastward on Tuesday. This
should allow the fog and stratus to remain to at least midday 
tomorrow. Have issued some freezing fog advisories until noon 
Tuesday for some of the lower elevation locations which can be 
expanded this evening based on ongoing trends. Otherwise the 
weather should be fairly quiet until Wednesday when precipitation 
begins to spill east of the Cascades especially by late in the 
day. Heavy amounts of snow are expected in the Washington Cascade 
east slopes and potentially the Kittitas valley Wednesday night 
and Thursday. The East Slopes could see over two feet of total 
snow accumulation with the Kittitas Valley 6-8 inches. Wednesday 
night and early Thursday a wintery mix of rain freezing rain and 
some snow will be possible across the lower elevations as 
temperatures hover near freezing. However by Thursday afternoon 
most of this activity should change to rain. Winds will get rather
gusty in the Grande Ronde Valley Tuesday through Tuesday night 
with gusts to 50 mph...especially south of La Grande. A Wind 
Advisory has been issued for the Grande Ronde Valley. 78

LONG TERM...Thursday night through Tuesday. Rain and mountain snow 
will continue Thursday night with some freezing rain possible in the 
colder locations through the Yakima and Kittitas Valleys and down 
near Hanford.  Heights are rising on Friday with snow levels 
continuing to rise to near 4000 feet in the Washington Cascades and 
5000 feet from central Oregon through northeast Oregon/southeast 
Washington. On Saturday the plume of moisture becomes more 
north/south oriented with some drier conditions across eastern 
Oregon before the entire band of moisture shifts east Saturday night 
and Sunday. Models are consistent in keeping a band of moisture 
across central and northeast Oregon through Monday with some rain 
and snow showers possible. Temperatures will be warming through 
Friday to readings well above normal with the strong warm 
advection and then moderate to near normal through the rest of the
period. 

AVIATION...00z Tafs...LIFR/IFR conditions will persist for 
YKM/PSC/ALW/DLS/PDT in low stratus and fog overnight. Small 
improvements are expected again Tuesday late morning. Winds will be 
below 10 kts at all sites with VFR at RDM/BDN. 93 

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  23  34  22  37 /   0   0   0   0 
ALW  25  34  26  39 /   0   0   0  10 
PSC  24  33  24  37 /   0   0   0  10 
YKM  22  34  23  34 /   0   0   0  30 
HRI  22  33  24  37 /   0   0   0  10 
ELN  23  33  22  33 /   0   0   0  30 
RDM  19  38  23  43 /   0   0   0  10 
LGD  23  34  23  36 /   0   0   0   0 
GCD  22  36  22  39 /   0   0   0  10 
DLS  26  37  29  39 /   0   0  10  30 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Freezing Fog Advisory until noon PST Tuesday for ORZ044-507.

     Wind Advisory from 4 AM Tuesday to 4 AM PST Wednesday for ORZ049.

WA...Freezing Fog Advisory until noon PST Tuesday for WAZ026-027-029.

&&

$$

82/78/85