Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 261204

Area Forecast Discussion
National Weather Service Spokane WA
404 AM PST FRI DEC 26 2014

A vigorous low pressure system will produce widespread
accumulating snow Saturday into Sunday. The heaviest snow
amounts will likely occur over the Idaho Panhandle where amounts
of 5 to 9 inches will be a good bet by Sunday morning. Bitterly
cold northeast winds will develop by Monday morning. Temperatures
will be well below average most of next week as arctic high
pressure settles over the Inland Northwest.



Today and Tonight: A weak upper level disturbance will exit the
southern Idaho Panhandle this morning in the northerly flow. Look
for snow accumulations of an inch or less in the mountains of
southern Shoshone county and around Winchester/Craigmont mainly
before sunrise. Low clouds and fog will fill the sheltered valleys
of northeast Washington and north Idaho again this morning. With
very little wind expected today, low clouds and fog may be slow to
dissipate around Colville, Cusick, the Spokane River, and over
Lake Roosevelt. A good deal of sunshine is expected again today
over the Columbia Basin and East Slopes of the Cascades.
Temperatures exceeded all guidance yesterday at Wenatchee, Omak
and Moses Lake. It may be tough to have a repeat of the mid to
upper 40s again today, but it will be another relatively mild and
mainly sunny day for these areas. /GKoch

Saturday through Sunday night...Models continue to show an upper
low dropping out of British Columbia into the Inland Northwest
this weekend. During the bulk of the dynamics with this
system...strong mid level westerly flow will be present favoring
heavy snow accumulations for the Cascade crest and Idaho
Panhandle. However strong mid level forcing and favorable jet
support will favor moderate accumulations for much of Eastern
Washington as well. Northwest upslope flow into the Blue Mountains
and Camas Prairie will also yield significant snow accumulations.
During the initial event on Saturday...moist isentropic ascent
will overtake areas mainly east of a line from Republic to
Ritzville with widespread light to moderate precip developing.
Then Saturday night into Sunday morning the upper low drops
southeast into Northeast Washington and North Idaho. The potential
remains for a deformation zone to set up which could result in a
band of heavier snowfall like the 06z NAM and 00z UW WRF-GFS show.
The models are beginning to come into line (except the 00z gfs
which is further south) of the low tracking from near Kelowna, BC
southeast towards Sandpoint with this band of heavier precip
possibly developing somewhere between Ione to Deer Park stretching
east between Bonners Ferry and Coeur D`Alene. Confidence is low
with its precise location and intensity. On Sunday afternoon into
Sunday night the cold upper trough lingers, although dynamic lift
diminishes. This in combination with increasing N-NE winds
bringing in colder and drier air from the Northeast by Sunday
night will lead to a gradual decrease in snow showers.

*Snow Levels: Most areas will see just snow through this event.
 Although a tongue of warmer air will sneak into areas from
 Ritzville to Pullman south with snow levels rising to near 2500
 feet Saturday afternoon. However snow levels will fall again down
 to the valley floors overnight Saturday night as cooler air moves
 back into these areas.

*Snow amounts: Periods of snow will occur over a prolonged 36 hour
 duration. The heaviest accumulations will be in the Central
 Panhandle Mountains with 10-15 inches expected with the highest 2
 day snow totals in the mountains. The North Idaho Panhandle,
 Coeur D`Alene area, and Idaho Palouse will see 2 day snow totals
 of 5-10 inches. The Northeast Washington Mountains, Spokane area,
 and Washington Palouse will see 3-6 inches with the highest
 amounts near the Idaho border. The Blue Mountains and Camas
 Prairie may pick up 7-11 inches. Across the Columbia Basin and
 Lewiston area amounts are expected to be light...generally around
 an inch for Lewiston with little to no accumulation for the
 Wenatchee area, and Moses Lake area. Strong westerly flow will
 also favor only light snow amounts away from the Cascade crest
 including Plain, Leavenworth, and Winthrop.

*Winds: As the low moves into Northeast Washington into the North
 Idaho Panhandle Saturday night breezy winds will develop south of
 the low, especially on the palouse. This will lead to areas of
 blowing snow mainly above 3000 feet (Blue Mountains, locally on
 the Camas Prairie and Central Panhandle Mountains). High
 temperatures on the palouse in the low to mid 30s is expected to
 limit blowing snow potential.

*Hazards: Confidence remains high of snow creating hazardous
 travel conditions in the Idaho Panhandle. Snow will also lead to
 difficult travel over the Cascade Mountain passes, and over
 portions of Eastern Washington especially near the Idaho Border.

Monday through Thursday: The wind and cold temperatures on Monday
will produce cold wind chills. Northeast winds have been increased
Monday with sustained winds of 10 to 20 mph with gusts to 30 mph
common over much of the Inland Northwest. Stiff cold advection
and the likelihood of fresh snow cover over north Idaho and much
of Eastern Washington suggest that temperatures won`t warm much
through the day on Monday. Temperatures should remain well below
average most of next week. There should be an abundance of
sunshine Tuesday and filtered sunshine (through high clouds)
Wednesday. However, temperatures will struggle to climb into the
teens and low 20s Tuesday and Wednesday afternoon. /GKoch


12Z TAFS: Low stratus and fog will be problematic for Coeur
D`Alene, Spokane, Sandpoint, Colville, and Pullman today. Early
morning fog imagery derived from satellite shows a bit more
fog/stratus around Spokane than yesterday at this time. Light
boundary layer flow and a late December low sun angle will hinder
the dispersion of fog this morning. Fog lingered at Coeur D`Alene
and Spokane Felts until 20z yesterday. Our TAFs follow yesterday`s
trends, but may be optimistic since it appears the fog may be a
bit more widespread this morning. /GKoch


Spokane        34  25  32  27  31  18 /   0  20 100  90  60  40
Coeur d`Alene  33  24  31  27  31  17 /  10  20 100 100  60  40
Pullman        35  25  33  28  30  15 /  30  10 100  90  80  50
Lewiston       39  26  37  32  36  24 /  40  10  50  90  70  50
Colville       33  23  32  25  32  19 /   0  20  90  90  50  30
Sandpoint      32  24  31  26  31  17 /   0  30 100 100  60  20
Kellogg        31  23  30  25  30  15 /  20  20 100 100  80  40
Moses Lake     41  24  36  26  36  25 /   0  10  40  20  20  20
Wenatchee      41  25  39  26  35  26 /   0  10  20  30  10  30
Omak           35  22  30  23  30  20 /   0  10  20  50  30  30


ID...Winter Storm Watch from late tonight through Sunday morning for
     Central Panhandle Mountains-Coeur d`Alene Area-Idaho
     Palouse-Northern Panhandle.


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