Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 222337

Area Forecast Discussion
National Weather Service Spokane WA
337 PM PST Sun Jan 22 2017

A vigorous upper level disturbance will bring a mix of rain and
snow to the Inland Northwest tonight. Wet snow accumulations will
be possible for the Methow Valley, Waterville Plateau, and the
Okanogan Highlands. Snow showers will linger into Monday over far
northeast Washington and the Idaho Panhandle. A drier and cooler
weather pattern is expected next week with the possibility of
deteriorating air quality as the week wears on.


Tonight...Satellite reveals a cold occluded front wrapping into an
offshore low pressure is sweeping through the forecast area this
afternoon from south to north. It appears from web cams and
observations that the predominant p-type is snow above 2000 feet
elevation..with a mix or rain at lower elevations. Web cams in the
snowy areas suggest there is little sticking to road surfaces.
The snow level is expected to drop this evening as the front
passes...but little or no accumulation is expected below 2000 feet
in the basin. The precipitation shield will be moving through the
northern tier zones tonight...likely as all snow even down to
valley floors with minor valley accumulations. The best prospect
for significant accumulations continue to be over the western
zones where easterly low level flow into the cascades will augment
frontal lift as well as enhances lift over cooler air trapped in
the Cascades lee zones. The Winter Weather Advisories for the
high terrain of the western basin and the Cascades still look
valleys and will continue to expiration this evening.

After the frontal precipitation shield moves out to the north
overnight the main issue will be fog and low clouds with today`s
precipitation leaving a very moist low level air mass with light
winds. Also wet roads will likely freeze up overnight promoting a
slick morning commute for Monday. /Fugazzi

Monday through Wednesday night...As an area of low pressure off the
coast digs to the south and allows for a ridge of high pressure to
maintain closer residence near the coast. Issues of note coupled
with this pattern change include a leftover weakening frontal
boundary which allows for the highest pops to be focused over the
extreme northern third of the forecast area and near the British
Columbia border Monday. This frontal boundary slowly moves south and
the far western edge of it weakens and because of this pops Monday
night through Tuesday night remain generally confined to the North
Idaho Panhandle while most, if not all, Eastern Washington locations
remain dry or have considerably lower pops. Wednesday into Wednesday
night the ridge axis is over the coast and has a bit of a positive
tilt to it as it remains juxtaposed against lower pressure over
Central North America with the north to south path provided by this
setup allowing for minor pops to linger over North Idaho and the
Blue Mountains which could make use of disturbances dropping down in
this trajectory as it is somewhat favored as an upslope flow.
Forecast temperatures remain slightly on the cool side of normal
given the general cold trajectory this synoptic setup favors and
winds should be generally light as well. /Pelatti

Thursday through Sunday: The ridge of high pressure axis will
shift over the region during this period. Temperatures will warm
aloft Friday into the weekend, which will strengthen the
inversion. Little mixing is anticipated through at least Saturday
with strong subsidence and weak winds under the ridge. What little
wind we will have will be easterly out of the Palouse Friday and
Saturday. This may be enough to push the stratus across the
northern and western portions of the forecast area, but confidence
is low.

Air stagnation will be a potential issue. With that said,  the
inversion under the ridge will be at its strongest heading into
the weekend and the ECMWF is a bit stronger with a shortwave
disturbance on Sunday than the other medium range model guidance.
If the 12Z ECMWF guidance verifies, then this shortwave for
Sunday may be enough to generate some mixing. This scenario seems
to be more of an outlier at this point, and it is more likely
that the ridge will just flatten and begin to re-amplify for early
next week. Potential locations for the worst stagnant atmospheric
conditions will be central portions of WA from the east slopes of
the northern Cascades to the Okanogan Highlands and western
basin. Inversions at least through the end of the work week will
not be as strong as our last air stagnation event since we are not
being influenced by a modified Arctic air mass; thus, surface
temperatures are expected to be hovering more in the 20s under a
stratus deck than in the single digits and teens under clear
skies. /SVH


00Z TAFS: An occluded frontal band will pass from south to north
through the forecast area this evening bringing generally MVFR
ceilings and vis in -RASN to the eastern TAF sites except for
KLWS which will see occasional VFR ceiling rain showers. KEAT and
KMWH area largely behind the front but will likely experience IFR
and LIFR stratus and fg as skies clear after 06Z
tonight...continuing through Monday morning with some improvement
to MVFR stratus ceilings in the afternoon. The KGEG area TAF
sites will also develop IFR ceilings after precipitation shuts
down due to weak upslope flow and a very moist boundary layer.
KPUW and KLWS will benefit from low level drying easterly flow and
should be VFR Monday. /MJF


Spokane        27  34  24  31  19  30 / 100  10  10  10  10  20
Coeur d`Alene  29  34  23  32  20  31 / 100  10  30  30  20  30
Pullman        26  34  22  32  19  30 /  80   0  40  40  20  30
Lewiston       29  39  27  34  23  33 /  60   0  30  30  10  20
Colville       29  34  22  29  20  28 / 100  20  10  10  10  10
Sandpoint      30  34  23  31  21  29 / 100  30  20  30  20  30
Kellogg        27  33  21  29  19  29 / 100  10  40  40  30  40
Moses Lake     25  34  22  31  16  30 /  20   0  10  10  10  10
Wenatchee      28  34  25  28  17  28 /  20   0   0  10  10   0
Omak           29  33  24  30  15  29 / 100  20  10  10  10   0


WA...Winter Weather Advisory until 10 PM PST this evening above 1500
     feet for East Slopes Northern Cascades.

     Winter Weather Advisory until 4 AM PST Monday above 2500 feet
     for Okanogan Highlands.

     Winter Weather Advisory until 7 PM PST this evening above 2000
     feet for Waterville Plateau.


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