Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 242216

Area Forecast Discussion
National Weather Service Spokane WA
216 PM PST TUE NOV 24 2015

Light snow, with pockets of rain, will gradually decrease this
evening and tonight with increasing winds. The area is expected be
dry Wednesday, with locally breezy to windy conditions.
Thanksgiving through next weekend looks dry, with lighter winds.
Temperatures remain cool with an increasing chance of fog and low
clouds starting this weekend.


Tonight: Precipitation wanes and strong winds expand.

* Impacts: Slick roads from snow falling this afternoon, waning
  through the evening from the north. Refreezing of any melted
  snow/water on roads overnight and Wednesday morning for possible
  black ice on untreated roads and other walking surfaces for the
  morning commute. Strong winds expanding across portions of the
  region through the evening and continuing through the night,
  with possible blowing snow and wind chills dropping toward the
  single digits overnight/early Wednesday morning.

Low pressure continues to spiral south along the Pacific Northwest
coast, approaching the OR/CA border. This feature is expected to
pivot inland toward western NV through the night. The deformation
axis extending in eastern WA, which has been responsible for the
snow and rain, will be drawn south with that feature through
tonight. That shifting feature, the mid-level ridge flopping in,
and the drier north winds down the Okanogan and the northeast
winds strengthening through northeast WA and north ID will lead to
the declining precipitation threat through this evening. Through
the first few hours of the late afternoon snow showers linger
across the portions of the northern mountains and upper Columbia
Basin, Spokane and Coeur d`Alene area. Yet progressing into this
evening the threat will shift into the southern Palouse and
central Panhandle southward. Then by late evening and the
overnight the main threat is expected to shift to the Blue
Mountains and Camas Prairie and dwindle.

The current winter weather highlights that expire at 4 PM will be
allowed to expire then. Further south, winter weather advisories
over the Palouse will be allowed to continue through the evening.
As temperatures fall with the night the potential for the rain or
rain/snow mix to change to all snow will increase. So the
advisories will be allowed to continue. If this doesn`t materialize
or if the precipitation just shuts off the advisory may be ended
earlier. Similar thinking goes towards the Central Panhandle,
Blues and Camas Prairie advisories.

Winds then become the dominate weather concern, as well as some
cold wind chills. A tight north-to-south gradient between Canadian
high pressure and low pressure to the south develops, with an
approximately 16 mb gradient between the Canadian and Oregon
border per guidance. This and the associated CAA and slight mixing
within this region will lead to the stronger wind. The strongest
winds are expected to remain across the Okanogan Valley through
the western/upper Columbia Basin and through the Purcell Trench
due to channeling and expose terrain. Mean speeds around 15 to 25
mph with gusts up to around 40 mph are projected. Isolated spots
may border advisory speeds but these are expected to be isolated.
So we will hold off on issuing anything for it but it will be
monitored. Some of the mountain peaks could also see higher gusts
around 50 mph. Elsewhere winds will be breezy but the more
sheltered valleys may only see gusts around 15 to 30 mph. Places
like the L-C Valley may not see more than 20 mph gusts, if that.

With temperatures in the teens and 20s overnight and the associated
wind, these may produce some rather cold wind chills. Value could
drop toward into the single digits with some below zero wind
chills possible across some of the northern valleys. Additionally,
there may be the potential for some blowing snow. The
strengthening winds and any snow which lingers or has fallen
through the day will have opportunity to blow, potentially
reducing visibilities. However the snow may be too wet to
effectively blow so it is described as patchy.  Lastly, even with
the ending precipitation threat, travelers will have to think
about a refreeze of any snow or water on roads through the night.
This could lead to some areas of black ice and could once again
mean a dangerous or slower commute for some, especially on
untreated roads. /J. Cote`

Wednesday through next Tuesday...The current storm system bringing
precipitation to much of the region will be gone by dawn on
Wednesday with the forecast area subject to breezy to locally
windy conditions as a cold polar air mass invades the forecast
area from Canada. The windiest areas will be near the mouths of
major north-south valleys such as the Okanogan Valley and Purcell well as the upper Columbia Basin where the cold dense
air will gather momentum over the descending elevations toward the
deep basin. Some patchy blowing snow can be expected along the
I-90 corridor Wednesday morning. Otherwise the wind chill will be
rather the single digits across much of the
area...until winds slacken off Wednesday evening.

For the remainder of the extended forecast models are in decent
agreement in developing a Rex Block over the region...which is a
pattern very conducive to dry and cool conditions with
deteriorating air quality in the valleys and a gradual increase
of fog and low clouds through the upcoming week. This blocking
pattern will almost certainly remain locked over the region
through the weekend and into early next week...with the beginnings
of a break down possibly by the middle of next week but this
prospect is very uncertain and low confidence. /Fugazzi


18Z TAFS: Low pressure will push into Oregon this afternoon. This
will send up moisture from the south while an Arctic front pushes
down from the north. Expect light snow to continue through about
00Z this afternoon at KGEG, KSFF and KCOE. Much of this snow will
be very fine and result in light or little accumulation, especially
in the afternoon. Northerly winds will strengthen through today
and into tonight down the Okanogan Vly and through the Purcell
Trench with gusts to around 30 mph expected. A brief period of
light snow will be possible at KPUW and KLWS this evening as the
thermal profiles cool with the northerly winds. Cigs and vis will
steadily improve through the day and into tonight from north to
south. /SVH


Spokane        22  31  15  30  16  29 /  20   0   0   0   0   0
Coeur d`Alene  18  29  15  31  15  31 /  30   0   0   0   0   0
Pullman        24  31  15  29  16  30 /  60  10   0   0   0   0
Lewiston       26  35  18  32  17  32 /  60  10   0   0   0   0
Colville       18  32  12  34  14  34 /  10   0   0   0   0   0
Sandpoint      16  28  15  30  16  31 /  20   0   0   0   0   0
Kellogg        16  26  12  28  13  29 /  70  10   0   0   0   0
Moses Lake     26  35  15  33  17  35 /  20   0   0   0   0   0
Wenatchee      22  35  19  34  20  34 /  10   0   0   0   0   0
Omak           18  32  14  32  18  33 /  10   0   0   0   0   0


ID...Winter Weather Advisory until 10 PM PST this evening for Central
     Panhandle Mountains-Idaho Palouse.

     Winter Weather Advisory until 4 AM PST Wednesday for Lewis and
     Southern Nez Perce Counties.

     Winter Weather Advisory until 4 PM PST this afternoon for Coeur
     d`Alene Area-Northern Panhandle.

WA...Winter Weather Advisory until 10 PM PST this evening for Lower
     Garfield and Asotin Counties-Washington Palouse.

     Winter Weather Advisory until 4 AM PST Wednesday for Northeast
     Blue Mountains.

     Winter Weather Advisory until 4 PM PST this afternoon for
     Northeast Mountains-Okanogan Highlands-Spokane Area.


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