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fxus66 kotx 251733 
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Area forecast discussion
National Weather Service Spokane Washington
933 am PST Sat Feb 25 2017

Synopsis...
snow will return to the inland northwest tonight, Sunday, and
Monday. A prolonged period of snow showers will have the potential
to produce significant accumulations for the Idaho Panhandle and
portions of southeast and East Central Washington. Chilly
temperatures will linger through Tuesday. A windy weather pattern
will be possible Wednesday through Saturday.

&&

Discussion...

..widespread light to moderate snow accumulations tonight...
Sunday...and Monday...

Today: it will be another chilly day for the inland northwest. We
have entered late February and our high temperatures should be in
the low to mid 40s. The best we will be able to muster this
afternoon will be the 30s for most areas. Scattered snow showers
are expected throughout the day over the Idaho Panhandle, but not
as widespread as they were yesterday. A transient high pressure
ridge will build over the Pacific northwest today, but there will
be enough shallow instability for convective snow showers for
Kellogg, St Maries, Lookout Pass, and over the high terrain around
Sandpoint. Areas of fog around Coeur D'Alene, Spokane, and
Davenport should dissipate by mid to late morning. With chilly
temperatures aloft, our morning inversion will be relatively weak.
We will also see increasing southwest winds improving low level
mixing by afternoon ahead of low pressure moving in tonight.

Tonight through Sunday night: a slow moving low pressure system
will arrive tonight and linger over the inland northwest through
Monday. The evening model runs are in decent agreement that the
center of a 500mb low will track southward along the b.C. Coast
overnight reaching the Washington coast by early Sunday morning.
After midnight, the inland northwest will be under an increasingly
difluent flow aloft as a surface pressure trough develops over
south central and southeast Washington. Light snow accumulations
will be possible region-wide from the pre-dawn hours Sunday
through Sunday evening. At this time it looks like the best
combination of moist isentropic ascent, low level surface
convergence in the vicinity of the developing surface trough, and
steepening lapse rates will occur over the Palouse, Spokane area,
and the central Idaho Panhandle from early Sunday morning through
Sunday afternoon. If these elements come together as advertised,
accumulations of 2 to 4 inches will be possible for the
aforementioned areas with localized accumulations of 6 inches or
more. The convective (showery) nature of the snow on Sunday will
contribute to high variability in snow amounts. With 500mb
temperatures in the -32c to -34c range, some spots under the
heaviest snow showers could receive upwards of an inch per hour
Sunday morning and Sunday afternoon. Travel will likely be
treacherous Sunday morning with Road temperatures below freezing.
Daytime warming on Sunday may lead to wet or slushy Road
conditions on well traveled roads during the afternoon with high
temps in the low to mid 30s.

The models suggest that snow showers will become less concentrated
over eastern Washington and the Idaho Panhandle Sunday night as
The Heart of the upper trough dives into Oregon. However, our
temperatures aloft will remain cold enough for localized moderate
to heavy snow showers. The combination of falling Road temps and
additional accumulations will raise concerns for treacherous
driving conditions Sunday evening through Monday morning. /Gkoch

Monday through Thursday...interval starts out with a cold trof
containing conditionally unstable air lingers over the Pacific
northwest. A clutter of shortwave disturbances dropping down
northwest to southeast in the flow will favor the highest pops over
extreme southeast Washington and the north Idaho Panhandle Monday
and Tuesday. Tuesday night through Thursday the flow becomes more
zonal and the jet stream is drapped across northern border and as
such the wind is substantially increased allowing for quite windy
and gusty conditions. The positioning of this upper level jet will
also favor a snow shadow off the Cascade crest that extends across
the Columbia Basin and some lowlands in the periphery. Forecast
temperatures on the cold side of normal for this time of year remain
valid with the cold trof Monday through Tuesday followed by the
mixing brought about by the close proximity of the jet stream allows
for warming resulting in temperatures closer to or slightly on the
warm side of normal Tuesday night into Thursday. /Pelatti

Friday and Saturday...the region remains in west-northwesterly
flow aloft during this period with a strong jet stream that will
work its way overhead by late Friday and into Saturday. As far as
precipitation, this would favor the Cascade crest and Idaho
Panhandle for the bulk of the precipitation with a decent rain
shadow in the basin. Perhaps the bigger issue however will be the
wind potential during this period. Models show the main wave pass
to our north with associated deepening surface low over British Columbia and
Alberta and trailing cold front. This leads to a sharp tightening
of the pressure gradient, which combined with the strong momentum
aloft, could lead to a windy scenario late next week and early
weekend. Continued the trend of increasing wind over the previous
forecast, but may still be too conservative if current model
solutions end up verifying. Certainly something that will be
monitored over the next week. /Kalin

&&

Aviation...
18z tafs: areas of low clouds and patchy fog over the Columbia
Basin...Spokane/Coeur D'Alene area...and Palouse will lift this
morning. But afternoon heating and a moist boundary layer will
produce a stratocumulus deck this afternoon with MVFR conditions
expected at kgeg/ksff/kcoe/kpuw. Mixing will be on the increase
through the afternoon ahead of an approaching low pressure system.
Snow will develop late this evening into the overnight hours for
the region. The most steady snow with lower visibilities is
expected at Spokane, Coeur D'Alene, Sandpoint, and Pullman. 1 to
3 inches is expected at these airports by 18z Sunday. For
keat/kmwh up to an inch is expected...while at klws marginal
temperatures for accumulating snow may result in only a dusting.
Jw

&&

Preliminary point temps/pops...
Spokane 32 24 33 24 33 20 / 10 80 90 60 40 20
Coeur D'Alene 33 23 32 23 34 16 / 20 80 90 70 50 50
Pullman 34 26 33 24 35 22 / 10 60 100 60 70 60
Lewiston 41 29 37 28 40 28 / 10 30 70 60 60 50
Colville 34 23 34 18 34 18 / 10 50 60 40 30 20
Sandpoint 32 23 32 23 33 18 / 20 70 90 60 60 40
Kellogg 30 24 31 25 32 21 / 30 80 100 80 80 80
Moses Lake 36 24 37 18 38 21 / 0 50 70 40 20 20
Wenatchee 35 24 37 20 35 21 / 0 30 70 40 20 20
Omak 34 23 35 19 35 18 / 0 50 60 30 10 10

&&

Otx watches/warnings/advisories...
Idaho...none.

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