Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 180918

Area Forecast Discussion
National Weather Service Missoula MT
318 AM MDT Fri Oct 18 2019

.DISCUSSION...Currently there are scattered showers from northern
Idaho and Clearwater Counties, through Missoula and the Mission
valleys. As a weak front passes through our area between 5am in
northwest Montana and 10am in southwest Montana, expect a brief
but intense period of precipitation. In addition, winds will shift
from the southwest to more westerly and become quite breezy in
the afternoon. The valleys could see gusts to 30 MPH, while higher
terrain could see gusts to 50 MPH. Consequently, we have issued a
lake wind advisory for the Flathead Lake through 6pm this
evening, however any boaters should use caution on any area lakes

Mountain Passes like Lookout and Lolo are currently sitting
at freezing, the precipitation they will see will be in the form
of snow. Road temperatures are above freezing, so beyond reduced
visibility no impacts are expected currently through the evening

Snow levels will fluctuate through Friday but accumulating snow
will only initiate overnight Friday. A more dynamic weather
system will pass through Central Idaho on Saturday. This will
bring more prolonged and widespread precipitation for the entire
forecast area Saturday. Precipitation amounts in Central Idaho
will range from .5 in lower elevation to an inch in higher
terrain. While valleys of Montana will see a .25 to .5 with
locally higher amounts in terrain. In addition snow levels that
will remain fairly constant will begin to drop overnight Saturday.
A change over or mix with snow in valleys as low as 3000 is not
out of the question with no accumulation expected.

Snow accumulations of 8 to 12 from Saturday morning through
Sunday morning are possible for Lookout and Lolo passes, with
higher amounts in terrain of Central Idaho, hence a winter storm
watch is in affect above 4000 for the Southern Clearwater

Monday another atmospheric river will move into the region from
the west accompanied by a warm front. This will cause snow levels
to rise quickly and reach 6,000 to 7,000 feet by Tuesday morning.
As a result snow impacts from this system are expected to be
minimal. Some passes like Lookout, Lolo, and Lost Trail will see
some snow with this system, but through the morning Monday the
snow will become slushy and wet. Lookout and Lolo passes are
aligned better with the atmospheric river and the mountains to get
more precipitation, so they will likely be the most affected by
snow Monday morning.

Models disagree on the timing of the next cold front, but right
now it looks like Wednesday or Thursday snow levels will come
crashing back down to the valleys and the weather pattern looks to
remain active.


.AVIATION...Scattered showers currently from MSO to GPI as a wave
is approaching our area affecting terminals between 18/1000 and
18/1500z. This will be accompanied by a short but intense period
of showers, decreasing ceilings and visibility temporarily.
Breezy southwest winds will shift westerly with the passage of the
wave. Expect afternoon gusts of 25 MPH at GPI and MSO, while SMN
and BTM could be as high as 30 MPH. After 18/1500z most shower
activity will be restricted to higher terrain, causing terrain
obscurations. Saturday will bring a more dynamic weather system,
with prolonged and widespread precipitation and lower ceilings.


MT...     Lake Wind Advisory until 6 PM MDT this evening Flathead/Mission

ID...Winter Storm Watch from late tonight through Sunday morning
     ABOVE 4000 FEET for the Southern Clearwater Mountains.


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