Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 232350

Area Forecast Discussion
National Weather Service Spokane WA
350 PM PST Thu Feb 23 2017

A cool and unsettled pattern will continue over the Inland NW
right into the weekend and into early next week. The main
precipitation threat will be mainly mountain based snow showers,
but a stronger system on Sunday may bring minor snow accumulations
to the valleys and Basin. Temperatures will be cooler than normal
for this time of year with overnight lows in the teens and 20s
and daytime highs only in the 30s. A gradual warm up is forecast
by the middle of next week.


Tonight through Saturday...Satellite indicates a broad upper level
trough over much of the western United States. Eastern Washington
and north Idaho sit under the western flank of this trough subject
to a series of spur waves descending out of Canada and rounding
the edge of the parent trough. The next of these waves will drop
through the northerly flow tonight and Friday. The dynamic foot
of this wave will be focused offshore as it passes but the surface
development under this wave will create some easterly upslope
flow into the Cascades tonight and Friday...while over the rest
of the area cold air aloft will destabilize the air mass Friday
afternoon and evening. This adds up to a small chance of snow
showers...and they will be snow rain expected for a
while in this cooler than normal inter-trough air mass...over
much of the region Friday and Friday evening. the best
concentration will be over the Cascades and the northeast
mountains...with some flurries possible in the basin.
Otherwise...between cellular showers sunbreaks are expected Friday
after another round of morning fog and low clouds.

Friday night and Saturday the latest wave will be moving out of
the region...digging into the Great Basin and any residual snow
showers will mainly impact the Idaho Panhandle mountains and the
Palouse. On Saturday dry northerly flow returns between spur waves
with a better chance of sunshine over much of the region...but
still cool with daytime highs struggling to achieve the mid 30s.

Despite the threat of snow showers any accumulations from these
short lived shallow convective cells will be negligible and
spotty. /Fugazzi

Saturday night through Monday: An upper level trough will be over
the region with a northerly jet in the easterly Pacific. A
shortwave trough pivots across the Pacific NW with a cold and
unstable air mass in place. The main dynamics slide along the west
side of WA, although a minor wave will spread east of the
Cascades and encompassing eastern Washington Sunday afternoon and
night as 500mb temps bottom out between -30 to -35C. Weak
isentropic lift increases Saturday night with an increase of
mid/high level moisture. This gradually decreases on Sunday as
instability increases from the passing shortwave. 850mb temps
around -6 which would mean snow at most locations, except for the
LC valley and southern Basin. The snow event looks to be begin
early Sunday morning and continue into Sunday evening as a weak
stationary boundary straddles the region. Snow accumulations look
to be light with 1-2 inches possible across much of the low lands,
while there is the potential of 2-3 inches the upper valleys in
north Idaho. This is a low end advisory concern and will monitor
it in upcoming model runs. A secondary wave clips northeast
Washington by Monday with renewed lift within the broad area of
instability and increased northwest flow. Sunday night into
Monday, the focus for snow will be across southeast Washington and
the central ID panhandle for another round of light accumulations
of 1-2 inches.

Monday night into Thursday: A more northwest flow aloft sets up
Monday night as a ridge takes a foot hold over the western U.S.
Temperatures will warm aloft as instability decreases. Isentropic
lift will also increase, especially by late Wednesday into
Thursday. Warming temperatures will be reflected at low levels
while snow levels rise to 2-3K ft on Wed and 3-4k ft by Thursday.
Light precipitation will increase across the orographic favored
locations of of the northern mountains, Idaho panhandle and
southeast Washington. This will bring light mountain snow for most
of the week. Valleys will see a light snow through mid week, then
a rain/snow mix by Thursday. Temperatures will stay below normal
and staying predominantly in the 30s through mid week, finally
peaking into the 40s by Thursday. /rfox.


00Z TAFs: Fog and stratus development are expected tonight over
the KGEG...KSFF and KCOE TAF sites as the cold air mass decouples
overnight. Overrunning clouds from a weak system off the coast may
help break the stratus between 16Z and 18Z into MVFR stratocumulus
ceilings with a small chance of -SHSN during the afternoon hours.
It is uncertain and low confidence forecast for a return of
stratus to KPUW overnight tonight with the favorable upslope
westerly winds expected to weaken and shift more southerly
overnight which would favor less of a threat for IFR conditions by
Friday morning. KLWS is expected to remain VFR overnight as is
KMWH and KEAT. During the day Friday upslope low level flow into
the Cascades will allow thickening and lowering ceilings at KEAT
and may deteriorate to MVFR during the afternoon with -SHSN
developing near the TAF site. /MJF


Spokane        18  34  19  34  24  34 /   0  10  10  10  30  60
Coeur d`Alene  17  34  16  34  22  34 /   0  10  10  10  50  60
Pullman        20  36  20  36  25  36 /   0  10  10  20  30  60
Lewiston       25  40  25  41  27  40 /  10  10  10  20  20  60
Colville       18  35  18  35  24  35 /   0  20  10  10  30  60
Sandpoint      19  33  17  34  23  33 /   0  20  10  20  50  60
Kellogg        19  33  18  33  23  33 /  10  20  10  20  50  70
Moses Lake     18  35  19  35  25  36 /   0  10  10   0  20  30
Wenatchee      20  32  19  34  24  35 /   0  20  10   0  30  40
Omak           19  32  19  32  24  33 /   0  20  10   0  40  50



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