Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 290505

Area Forecast Discussion
National Weather Service Spokane WA
904 PM PST FRI NOV 28 2014

A showery and breezy weather pattern will continue over far
eastern Washington and the Idaho Panhandle tonight, but snow
levels will remain above pass levels for motorists traveling. A
strong push of cold arctic air will bring very windy conditions
to the Okanogan Valley tonight and Saturday. Cold conditions, with
a few minor snow bearing weather disturbances, are forecast for
the upcoming work week.


Evening update: the arctic front is on the move. The main push of
colder air is making it into the Cascades and Okanogan, while it
remains mild over the southeast half of the forecast area. For
example at last report around 8 pm temperatures were in the mid-20s
near Oroville, WA over the northern Okanogan Valley, with north
winds sustained between 20 and 30 mph; at the same time Lewiston,
ID was at 56 degrees, with winds around that area coming out of
the southwest at around 15 to 25 mph with gusts to 45 mph.

So those winds have been blowing down the Okanogan Valley at a
good clip already, so I went ahead and started the wind advisory
in that area about an hour ago (730 PM). That portion of the wind
advisory also includes the Waterville Plateau, but those winds
should materialize later (after about 09-12Z).

The other wind advisory goes through midnight (12 AM) across the
Upper Columbia Basin east into the Spokane area and Palouse and
L-C Valley, as well as the Coeur d`Alene area (which I added at
730 PM to due to some rather strong winds reported at the surface
and indicated by radar aloft). Newest model runs support this
downward trend. These updates to the wind advisory are already on
the street. I did increase winds down the Purcell Trench tonight
into Saturday, as that increasing northerly gradient develops, but
these really don`t appear should increase until after 09-12Z).

The other issue out there is the precipitation. A modest shield
of rain continues to rake the eastern third of WA and north ID,
especially from the Palouse east into the portions of the central
Panhandle. All models support this precipitation gradually
decreasing from the northwest overnight. On the backside of this,
however, will be some some snow threat.

The rain changed to snow around the Okanogan Valley, per the ASOS
at OMK, around 5pm and fell for a couple hours. It wasn`t being
sampled well by radar and available web cams in the region did not
show much. Yet I have no reason to doubt the sensor. So this
highlights that some snow threat will be coming on the heels of
the cold front and with the cold core of the upper trough. The
snow chances will found near the Cascades through the Okanogan
the remainder of this evening and above about 5-6kft farther east
and south. However later overnight into Saturday snow levels drop
toward valley floors. Outside of the mountain the snow is not
expected to amount to much: a half inch or so over northeast WA
and north ID and maybe an inch to an inch and a half toward the
Palouse. More snow is projected about the Central Panhandle
mountains, where a snow advisory remains in place through the day
Saturday (4 am to 4 pm). The northwest flow and unstable upper
trough will help produce this threat here, while the unstable
upper trough will bring the light snow threat across the remainder
of eastern WA and north ID.

The last thing to mention that some guidance suggests is a
possible Puget Sound Convergence Zone in the westerly flow. It is
mainly the NAM/SREF which has this suggestion, which wants to show
some band of snow developing near the Chelan/Okanogan county
border overnight (after 09Z) and expanding east across northern
Douglas and Lincoln county through Saturday.  Typically a band of
precipitation associated with the PSCZ doesn`t spread that far
east, so I suspect there may be some mix of the incoming upper
trough influencing that depiction. /J. Cote`


00Z TAFS: Main focus through this period will revolve around
strong cold front dropping across the BC/WA border and a rapid
intensification of the precipitation shield over the area.
Confidence is high that all sites aside from MWH and EAT will see
periods of -ra...however bigger question is will cigs lower to
MVFR or worse. The longer the rain persists...the better the we placed these conditions in the GEG COE and PUW
forecasts but confidence isn`t terrific. The front will exit all
the sites before 12z Sat...with drier conditions expected. Other
concern this evening will be the strong winds and potential for
Low Level Wind Shear. The Spokane wind profiler is still showing
south winds about 1500 feet above the ground with speeds nearing
50 kts. Based on surface wind reports and forecasts this will
result in some wind shear but not enough to satisfy the necessary
criteria. The exception is at PUW where surface winds have been
quite erratic and much lighter than anywhere else nearby. Winds
will weaken overnight at most sites with the direction gradually
turning to more of a west-north direction. fx

NOTE: The VIS sensor at EAT is out of service so amendments to
VIS are not scheduled. The offending sensor replacement is on
order and may be returned to service by Saturday.


Spokane        29  29  12  24  13  27 /  90  40   0   0   0  10
Coeur d`Alene  32  32  11  25  13  29 / 100  50  10   0   0  20
Pullman        33  33  15  26  17  32 / 100  40  10   0   0  40
Lewiston       40  40  20  29  20  37 /  80  50  20   0   0  40
Colville       22  24   3  20   9  26 /  80  20   0   0   0   0
Sandpoint      24  29   5  21   8  26 / 100  50  10   0   0  10
Kellogg        28  30   4  22  11  28 / 100  70  20   0   0  40
Moses Lake     32  32  12  25  13  27 /  30  10   0   0   0  10
Wenatchee      32  32  14  23  12  27 /  20  10   0   0   0  10
Omak           25  25   2  18   8  24 /  30  10   0   0   0   0


ID...Winter Weather Advisory from 4 AM to 4 PM PST Saturday for
     Central Panhandle Mountains.

     Wind Advisory until Midnight PST tonight for Coeur d`Alene Area-
     Idaho Palouse-Lewiston Area.

WA...Wind Advisory until Midnight PST tonight for Lower Garfield and
     Asotin Counties-Spokane Area-Upper Columbia Basin-
     Washington Palouse.

     Wind Advisory until 10 PM PST Saturday for Okanogan Valley-
     Waterville Plateau.


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