Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 122243
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
243 PM PST Tue Dec 12 2017

.SYNOPSIS...
Strong high pressure will persist through Thursday night. The
lowlands of eastern Washington and north Idaho will continue to be
covered by low clouds while the mountains remain mild and mostly
clear. Chances for wintry precipitation increase Friday morning.
Unsettled weather expected through next weekend and early next
week with a good chance of light snow returning to the mountains.

&&

.DISCUSSION...

Tonight: A weak upper level disturbance will move over the top of
our strong high pressure ridge overnight giving the region a shot
of scattered snow flurries. As of 230 PM, this disturbance was
moving into northern British Columbia. Deep layer moisture will be
limited and the models produce very little precipitation overnight
into early Wednesday morning. However, the models do saturate the
dendritic layer (-10C to -20C) suggesting the potential for a
"seeder/feeder" flurries. At this time, the potential for freezing
drizzle looks relatively low. Winds near the top of the inversion
layer do not show the warm advection signal that was present over
Spokane this morning. It does not appear that there will be the
southwest boundary layer upslope wind either. Tonight`s
disturbance does not look strong enough to disturb the low cloud
deck under the inversion, so most places that are cloudy this
afternoon will likely be under low clouds at sunrise.

Wednesday and Thursday: Tonight`s upper level disturbance will
exit the southern Idaho Panhandle early in the day Wednesday. Some
light snow will be possible early in the morning. Given the lack
of moisture, any accumulations look to be a dusting at best around
Lookout Pass and the mountains of southern Shoshone county.

The upper ridge will rebound Wed and Thu. A light northerly
pressure gradient through the day on Wednesday may erode some of
the low cloud deck around Northport, Kettle Falls, Republic, and
Oroville by afternoon. Elsewhere, high temperatures will likely be
similar to today. On Thursday, a weak easterly gradient may
produce a bit of clearing over the Idaho Palouse into Pullman. But
again, most lowland areas will be mired in clouds with afternoon
temps only reaching the upper 20s or low 30s. /GKoch

Wednesday night through Thursday night: The strong ridge of high
pressure will prevail through Thursday night with widespread low
clouds, patchy freezing fog and light winds. Mountains will remain
milder than the valleys. Dry conditions continue.

Friday through Monday: A pattern change will arrive by Friday
morning, a bit later than previous forecast. The ridge of high
pressure flattens by a low pressure trough rolling across southern
Canada. A weak frontal boundary limps east of the Cascades with
light precipitation for Friday. Snow levels will be on the rise
although sub freezing temperatures found in the valleys, from the
lee of the central Cascades, across the Columbia Basin into the
Palouse and LC Valley. This area has the potential of a wintry mix
of precipitation with a a slight chance of freezing rain. By
afternoon, low level mixing increases with west to southwest winds
and surface temperatures will moderate leading to more valley rain
and mountain snow for Friday afternoon and night. A new
development in the models is the ridge of high pressure amplifying
off the coast. This leads to a northwesterly flow aloft and a
better chance of orographic precipitation across southeast
Washington and north Idaho. By Saturday, the ridge presses inland
albeit dirty with more mid level moisture streaming overnight.
Light orographic snow will continue in the mountains. Chances
increase for Sunday and Sunday night with the passage of a weak
impulse across southern BC leading to the potential for more light
snow in the mountains. Monday looks drier in the west northwest
flow aloft and it`s based on the timing and track of the next low
pressure trough that will take shape by the middle of next week.
Temperatures will trend milder into the weekend and early next
week. /rfox.

&&

.AVIATION...
06Z TAFS: Low layer of stratus filling in the lowlands and valleys
with the tops generally around 1500 feet AGL or less to change
little into Tuesday. Some patchy fog noted around the edges of the
stratus as well with the primarily impact being the low IFR ceilings
caused by the stratus. A repeat of northeast winds tomorrow may
allow for another retreat of stratus along the north and east
edges and allow for breaks during the afternoon and early evening
at KGEG, KSFF, KCOE, and KPUW  /Pelatti

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        28  25  31  25  30  27 /   0   0   0   0   0   0
Coeur d`Alene  31  25  33  25  32  27 /   0   0   0   0   0   0
Pullman        31  25  33  23  33  27 /   0   0   0   0   0   0
Lewiston       30  27  34  25  34  30 /   0   0   0   0   0   0
Colville       30  28  31  28  30  28 /   0   0   0   0   0  10
Sandpoint      32  20  33  17  31  25 /   0   0   0   0   0   0
Kellogg        31  21  31  19  32  26 /   0   0   0   0   0   0
Moses Lake     33  28  33  30  32  27 /   0   0   0   0   0  10
Wenatchee      32  28  32  29  32  28 /   0   0   0   0   0  10
Omak           32  29  33  30  32  29 /   0   0   0   0   0  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Air Stagnation Advisory until 10 AM PST Friday for Central
     Panhandle Mountains-Coeur d`Alene Area-Idaho Palouse-Lewis
     and Southern Nez Perce Counties-Lewiston Area-Northern
     Panhandle.

WA...Air Stagnation Advisory until 10 AM PST Friday for East Slopes
     Northern Cascades-Lower Garfield and Asotin Counties-Moses
     Lake Area-Northeast Blue Mountains-Northeast Mountains-
     Okanogan Highlands-Okanogan Valley-Spokane Area-Upper
     Columbia Basin-Washington Palouse-Waterville Plateau-
     Wenatchee Area.


&&

$$


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