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Area forecast discussion 
National Weather Service Spokane Washington
443 PM PDT Thursday Aug 27 2015

Synopsis...
a cold front will approach the region tonight through Friday
night. This will result in breezy conditions Friday afternoon with
any showers expected to remain in the Cascades. Cold front passage
on Saturday will bring the potential for high winds. This will
create a situation for blowing dust with reduced visibility. Some
areas may also experience toppled trees and downed power lines. A
cooler and occasionally breezy regime with some shower activity
will persist through the next week.

&&

Discussion...

Tonight through Friday night: the region will be sandwiched
between a deep closed upper level low pressure system out at
140w/40n in the eastern Pacific and a ridge of higher pressure
over the rocky mtns. This will keep the region under broad
southwest flow. Satellite imagery does show a batch of moisture
pumping up on the eastern flank of the upper low, but much of this
is expected to remain west of the Cascade mtns. The east slopes of
the northern Cascades will see an increasing chance for showers on
Friday with the best chances remaining near the crest. The rest of
the region will see increasing high clouds. Pre-frontal winds will
increase on Friday as well. This will result in breezy southerly
winds, especially up the Okanogan Valley. Temperatures will be a
little cooler compared to today with the increasing cloud cover,
but high temps will still be in the 80s for most locations.

..strong storm system to bring high winds and blowing dust on
Saturday...

Saturday: the low situated off the coast will eject toward the
region in the morning. This storm system will feature a strong
vorticity maximum fueled by a 120 kt upper level jet. The surface
low will track into western Washington Saturday morning and then push
northeastward into southern British Columbia through the afternoon. Models have
been consistent in showing a strong cold front passage over the
inland northwest. The cold front is expected to push into the
basin Saturday morning then track up to the Canadian border
between noon to 2 PM.

* Winds: very strong winds are expected with frontal passage.
Models show 850 mb winds of near 50 kts across the Columbia
Basin with strong cold air advection. This is expected to result
in good momentum Transfer to the surface with 50-60 mph gusts
possible. These stronger gusts will be most likely with frontal
passage in the morning to early afternoon. Windy conditions will
likely persist through the afternoon; although 50+ mph gusts
will become less likely by this time with the front pushing
into Canada. We will be issuing a high wind watch for much of
the region; the exception will be the east slopes of the
Cascades and the Wenatchee area where the orientation of the
pressure gradient will not be as favorable for high winds. High
winds may result in pockets of toppled trees and/or downed power
lines. Strong cross winds along Interstate 90 between Vantage
and Sprague and Highway 2 west of Wenatchee to Spokane can be
expected. This will create hazardous driving conditions for high
profile vehicles.

* Blowing dust: strong winds are expected to pick up and blow
around a lot of dust across the Columbia Basin. Blowing dust
will be a concern as far east as the Spokane/Coeur D'Alene areas
and the Idaho Palouse. There is also a good chance for blowing
dust on the Waterville Plateau and up the Okanogan Valley.
Widespread visibility restrictions down to 1 mile will be
possible and some areas could see near zero visibility at times.
This will include the I-90 and highways 97, 2, 395, 195 and 95
corridors.

* Precipitation: models have been trending the heaviest rainfall
further west. It looks like the best chances for more
significant rainfall of 0.25-0.50 inches will be in the east
slopes of the northern Cascades. Areas closer to the Cascade
crest may see rainfall totals between 0.50-1.00 inches. This
rainfall will be stratiform in nature. This will translate into
some pockets of more moderate rainfall at times. High intensity
rainfall typically found with thunderstorms is not expected.
Some minor mud flows may be possible near burn scars, but the
risk for flash flooding looks low. /Svh

Saturday night through Thursday...general long-wave trof of low
pressure allows the jet stream to remain in close proximity which
is favorable to allow numerous shortwave passages through eastern
Washington and northern Idaho, and as such below normal
temperatures with above normal precipitation (but not excessive)
mark this forecast interval. Of significant note is a synoptic
scale low pressure system that nests in the large trof and digs
southward into it Wednesday and Thursday which helps to intensify
it and keep it in the area. Current timing shows the most robust
synoptic scale and smaller shortwave disturbances to move through
it and bring the best chances of precipitation to eastern
Washington and north Idaho Sunday and Wednesday. This pattern
change won't end the fire season for eastern Washington and
northern Idaho but will slow it down some. /Pelatti

&&

Aviation...
00z tafs: the region will be sandwiched between low pressure in
the eastern Pacific and high pressure over the rookies. A cold
front will linger offshore through Friday afternoon. The
proximity of the front will promote better mixing. This is
expected to result in continued smoke improvement at the taf sites.
However, MVFR visibility will be possible due to smoke at kgeg,
ksff, kcoe, kpuw and klws as inversions set in overnight. /Svh

&&

Preliminary point temps/pops...
Spokane 61 84 63 80 53 72 / 0 10 10 20 30 50
Coeur D'Alene 57 84 59 81 51 71 / 0 10 10 30 20 40
Pullman 55 84 59 83 51 73 / 0 10 10 20 20 20
Lewiston 64 89 66 89 58 81 / 10 10 10 20 20 20
Colville 55 83 56 79 49 72 / 0 10 10 50 30 40
Sandpoint 51 83 54 81 48 69 / 0 10 10 40 30 50
Kellogg 55 86 56 82 48 71 / 0 10 10 30 30 30
Moses Lake 60 85 62 77 55 75 / 0 10 10 20 30 30
Wenatchee 67 83 65 74 57 73 / 0 10 20 30 40 20
Omak 61 81 62 75 51 71 / 0 10 20 30 40 30

&&

Otx watches/warnings/advisories...
Idaho...high wind watch from Saturday morning through Saturday evening
for central Panhandle mountains-Coeur D'Alene area-Idaho
Palouse-Lewis and southern Nez Perce counties-Lewiston area-
northern Panhandle.

Washington...red flag warning until 8 PM PDT this evening for East Washington
central Cascade valleys (zone 677)-East Washington
northeast (zone 686)-East Washington northern Columbia
Basin (zone 673)-East Washington Okanogan Highlands (zone
687)-East Washington Okanogan/Methow valleys (zone 684)-
East Washington Palouse and Spokane area (zone 674).

High wind watch from Saturday morning through Saturday evening
for lower Garfield and Asotin counties-Moses Lake area-
northeast Blue Mountains-northeast mountains-Okanogan
Highlands-Okanogan Valley-Spokane area-upper Columbia Basin-
Washington Palouse-Waterville Plateau.

&&

$$

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