Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 220940

Area Forecast Discussion
National Weather Service Missoula MT
340 AM MDT Fri Sep 22 2017

...Difficult travel across southwest Montana and Lemhi County
above 5000 feet through today...

.DISCUSSION...A cool low pressure system will continue to lift
northward into north central Idaho through this morning. Moisture
continues to feed around this circulation, producing widespread
precipitation across primarily southwest Montana and Lemhi County.
Snow levels continue to drop this morning, with snow just
beginning to be reported in Butte, MT. Snow levels should lower
to roughly 5000 feet for this morning, which will lead to slick
roadways through much of the day, particularly for high elevation
passes (MacDonald Pass, Lost Trail Pass, Homestake Pass) as well
as un-paved backcountry roads. As the system continues to lift
northward, precipitation will also shift a bit farther north,
reaching along and south of a line from Lolo Pass to Missoula to
Great Falls. Far northwest Montana and much of central Idaho are
expected to remain dry.

In addition to precipitation, northerly winds will continue to
develop and strengthen in response to this weather system across
all of western Montana. Winds will gust as high as 30 mph at
times through this morning, before slowly weakening this
afternoon. The combination of wind and snow across southwest
Montana will cause periods of lowered visibility, which could make
travel difficult at times.

Precipitation will begin to decrease across the area starting this
evening, though light precipitation will likely continues near the
Continental Divide into Saturday morning. Lingering and clouds
with a few showers will be possible for Saturday.

Clear skies overnight on Saturday will bring the potential for a
hard freeze to occur Sunday morning for many valleys of western
Montana and also north central Idaho. Temperatures will be in the
mid 20s to mid 30s Sunday morning, so if you have sensitive
vegetation you wish to protect, please do so Saturday evening.

Sunday itself will be dry, as will most of next week, with plenty
of sunshine to go around under developing high pressure. The one
exception will be a brief disturbance moving through this high
pressure on Tuesday, bringing about perhaps a few rain showers
here and there across NW Montana and along the spine of the
Continental Divide. All in all though, next week will be a nice
one. Temperatures will be warming steadily, reaching into the 70s
by Thursday and Friday.


.AVIATION...A low pressure system will continue to affect
primarily southwest Montana and Lemhio County in Idaho with
widespread precipitation through much of today. Snow levels
will continue to drop, reaching around 5000 feet by this morning.
Widespread terrain obscurations are expected. The most
significant impacts of low visibility and low ceilings due to
precipitation will continue to exist at KSMN through 22/1900Z and
at KBTM through 22/2300Z. There is a chance that low visibility
and low ceilings due to light rain may develop at KMSO 22/1400Z
onward. Otherwise, north and northeast winds in the 10 to 20 knot
range will be present at the ridgetops. Ridgetops will be mostly
obscured during the next 24 hours, particularly across southwest
Montana and Lemhi County Idaho.


MT...Winter Weather Advisory until midnight MDT tonight ABOVE 5000
     FEET for the Bitterroot/Sapphire Mountains...
     Butte/Blackfoot Region.

ID...Winter Weather Advisory until midnight MDT tonight ABOVE 5500
     FEET for the Eastern Lemhi County...Western Lemhi County.


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