Area Forecast Discussion
Issued by NWS Spokane, WA

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690
FXUS66 KOTX 051150
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
350 AM PST Mon Dec 5 2016

.SYNOPSIS...
Icy and slick conditions are possible early this morning with
colder temperatures. The next weather system will give the region
a glancing blow. Light snow is forecast for the Columbia Basin,
Palouse, and southern Idaho Panhandle Monday afternoon into
Monday night. Expect dry weather with some rather colder
temperatures. More snow will be on its way for Thursday into
Friday, and this snowy pattern may continue into the weekend.

&&

.DISCUSSION...
Today through Tuesday...We are looking at a fairly robust low
pressure system dropping down the Washington coast today then
inland through Oregon tonight and Tuesday, with most of the energy
staying west of the Cascades. Cross Cascade flow will result in
some slop over precipitation this morning near the crest. The 00z
models were in pretty good agreement showing a a surface low
crossing the Cascades late this afternoon and tracking east
through the lower Columbia basin through the night and into
Tuesday. The 06z NAM just came in with a little slower timing and
the 06z GFS is matching that trend. The NAM also holds the
surface low together though a majority of the day Tuesday instead
of filling like to previous run. So some minor changes to the
onset of the precipitation and the areas with the heaviest
accumulation. Temperatures well on the cool side of normal will
result in precipitation as all snow.

Up-sloping flow into the Cascades will result in increasing
chances of snow across the lower east slopes and into the western
Basin by late this morning, with the snow not likely reaching the
eastern basin and the Palouse until this evening. Light snow
accumulation of an inch or less will be possible south and west of
a line about Republic to Coeur d`Alene through Tuesday afternoon.
The heaviest accumulations will be mainly south of a line from
about Lucerne to about Clarkia with 1-2 inches for the Wenatchee
area, the Waterville Plateau, the Columbia Basin, and the Palouse,
3-6 inches for the Blue mountains, and 1-3 inches for the Camas
Prairie. With the exception of the lower east slopes most of the
snow should fall this evening and overnight, missing the afternoon
commute. We will have to take a closer look at the Cascade
valleys south of Lake Chelan and the Wenatchee area as the
heaviest snow will likely accumulate this afternoon and early this
evening.

As mentioned earlier temperatures will be about 3-5 degrees below
seasonal averages with highs in the mid 20s to lower 30s. Lows
tonight in the teens to lower 20s. Tobin

Tuesday night through Wednesday night: No way around it, it`s gonna
be cold - really cold. Temperatures across the Inland Northwest
will be the coldest of the season, so far. In the wake of the
departing weather system, dry northwest flow aloft will set up
over the region. Despite some renegade orographic snow showers
over the southern ID panhandle, most areas will experience
clearing skies. Some patchy freezing fog is possible in sheltered
Cascade valleys and around the LC valleys late Tuesday night into
early Wednesday morning. At the surface, high pressure will drop
from the Canadian Rockies into Montana and generate brisk north to
northeast winds that will usher in dry and cold continental air.
There is plenty of cold air across northern B.C. and the Yukon
territories. At this time, early Wednesday morning looks to be the
coldest period as winds weaken and many locations dip into the
single digits to lower teens, possibly even Spokane. Could even
see some colder readings in sheltered locations in the region
with a light snow cover. The last time the region has experienced
temperatures this cold was the first week of January 2016.
Daytime highs will rise into the teens to mid 20s which is 15 to
20 degrees below normal. High clouds will move in from the
southwest Wednesday which will help moderate temperatures a couple
of degrees, but another cold night is anticipated into early
Thursday morning.

Thursday through Friday night: Now for the snow and it looks to be
quite significant across much of the Inland Northwest. The medium
range models are showing more agreement on their solutions. The
upper level flow flattens out as a Pacific jet takes aim on the
West Coast with a tap on some subtropical moisture. A surface low
spins up off in the eastern Pacific will a strong warm front that
lifts in from the southwest. There looks to be a slower arrival of
this front as it crosses Oregon Wed night, and finally reaches
Washington on Thursday. It`s a classic pattern as the overrunning
of this moist, mild air over top of the dry, cold continental air
will lead to isentropic lift and good chance of precipitation.
And given the low snow levels and cold temperatures, snow is a
good bet in all areas. The warm front will slowly push across the
region Thursday into Thursday night, and then through north Idaho
by Friday morning. Meanwhile temperatures will be on the rise
through the period. Over a 24 hour period from midday Thursday to
midday Friday, liquid precipitation amounts are forecast to range
from 0.2" to 0.4" in the low lands and 0.5" to 0.8" in the
mountains. This will translate to significant snow amounts with
the potential of several inches in the lowlands and a half of foot
and more in the mountains. Uncertainties do remain on how fast
the warm arrives and what this will do to the precipitation type
and amounts. In addition, there is a small chance for a wintry mix
of precipitation with sleet or freezing rain especially from
parts of the Columbia Basin and the Cascade valleys. A cold front
will sweep through the region late Friday into Friday night with
increased west to southwest winds with more showery conditions in
the mountains. /rfox.

Saturday and Sunday: We remain in a showery regime for Saturday
and Sunday as multiple disturbances rotate through. The westerly
flow all weekend will provide a good rain shadow leaving the lee
of the Cascades and much of the basin drier, with snow showers in
the Cascades, Idaho Panhandle and northern mountains. Snow levels
will be up to 1500-2000 ft on Saturday into Sunday, before
dropping below 1000 ft to start next week. This means any precip
that does fall across the basin over the weekend will likely fall
as snow. After the weekend models diverge, but another shot of
frigid air looks likely. /bwilliams



&&

.AVIATION...
12Z TAFS: Skies remain clear early this morning with quite a bit
of dry air in the boundary layer...even with the wind switching
around to the south-southwest and will keep the mention of lower
cigs or vsby out of the forecast. Otherwise high clouds are moving
in from the west this morning as a weather system begins to move
into the region. This system will spread -SN into the region
beginning near 21-22z at KEAT before reaching KPUW/KLWS/KGEG
between 04-06z. MVFR conditions are expected to develop with the
onset of -sn with cigs/vsby likely dropping to IFR vcnty of KEAT
where the heaviest precipitation is expected to develop. Tobin


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        30  18  24   9  19  10 /  30  50  10   0   0  10
Coeur d`Alene  29  16  23   6  18   8 /  20  20   0   0   0  10
Pullman        32  21  26  12  22  12 /  30  70  30  10   0  10
Lewiston       35  23  30  16  25  14 /  20  70  30  10  10  10
Colville       30  16  24   9  21   8 /  20  10   0   0   0   0
Sandpoint      26  13  20   3  17   6 /  10  10   0   0   0  10
Kellogg        25  10  18   3  16   5 /  10  30  20  10  10  10
Moses Lake     35  22  31  13  25  15 /  40  70  10   0   0  10
Wenatchee      33  23  30  13  23  14 /  60  60  20   0   0  10
Omak           31  18  26   9  20  10 /  30  20   0   0   0  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$



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