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fxus65 kmso 191104 

Area forecast discussion
National Weather Service Missoula Montana
404 am MST Fri Jan 19 2018

Discussion...widespread showers continue this morning across
west-central/southwest Montana and north central Idaho. Most areas
have transitioned over to snow as temperatures dropped overnight.
And although additional snow accumulations will generally be
light, expect roads to be quite slick for the morning commute due
to a combination of slushy/wet snow and black ice. In addition,
areas of fog have developed, mainly across northwest and west-
central Montana, which will further limit visibility at times.
Snow showers will likely continue through the day today as the
atmosphere destabilizes area wide. However, further impacts to
roadways will generally be limited to mountain passes by this

Saturday will continue to be cool and showery, particularly in the
higher terrain. For valley locations, showers will be hit and
miss, though any snow accumulations will be light. Weak high
pressure builds over the region late Saturday into Sunday, which
should decrease shower activity for most areas. Some patchy fog
will be possible Sunday morning, though lingering cloud cover
should keep fog from becoming widespread. But we do expect snow
showers will once again increase overnight into Monday morning as
a quick moving weather feature is forecast to pass over the
northern rockies. The greatest accumulations will be experienced
throughout the higher terrain and especially along the
Idaho/Montana border. That being said, the snow level should
remain sufficiently low to allow minor valley accumulation as

Showers will decrease in coverage and intensity on Tuesday with
weak high pressure building over the area. But once again this
break in the weather will be brief with the region falling under
yet another moist flow aloft starting early Wednesday. In fact,
the unique southerly position of the upper level jet (stretching
from Boise NE to dillon) should present the northern rockies with
a favorable pattern for snow across most all elevations Wednesday
morning. Conditions will turn far more showery during the
afternoon with accumulations becoming quite sporadic by Wednesday
evening. On Thursday the main trough digs into the Pacific
northwest and slowly progresses inland through the western United
States into Friday and perhaps even Saturday.

While the details of this mid/late week system are still quite
challenging to forecast, we do identify this as a very favorable
pattern for accumulating snowfall across both mountains and
valleys alike. But unlike more recent storms, this one will be far
more convective with areas of heaviest precipitation focused
under parcels of instability and energy associated with the upper
level trough and not frontal or boundary features (cold/warm front
or Arctic boundaries). Thus snowfall accumulations will be far
less uniform and likely quite variable even only a few miles away.


Aviation...widespread light snow showers continue this morning,
generally along and south of a line from kmlp to kmso to khln.
Most locations have cooled enough to bring snow even into the
lower elevations. Expect the terrain to be obscured due to lowered
ceilings and visibility in snow showers. In addition, areas of
valley fog have developed, primarily across northwest Montana,
north central Idaho and along the i90 corridor from Lookout Pass
to Drummond. Fog will likely persist through much of the morning.
The atmosphere becomes unstable this afternoon, which will favor
the development of snow showers across all of western Montana and
central Idaho.


Mso watches/warnings/advisories...
Montana...Winter Weather Advisory until 11 am MST this morning
Bitterroot/Sapphire Mountains.

Winter Weather Advisory until 11 am MST this morning
Potomac/Seeley Lake region.

Winter Weather Advisory until 11 am MST this morning
Butte/Blackfoot region.

Winter Weather Advisory until 11 am MST this morning
Missoula/Bitterroot valleys.

Idaho...Winter Weather Advisory until 10 am PST this morning above 3000
feet for the Orofino/Grangeville region.

Winter Weather Advisory until 10 am PST this morning southern
Clearwater Mountains.

Winter Weather Advisory until 11 am MST this morning western
Lemhi County.

Winter Weather Advisory until 10 am PST this morning above 3000
feet for the lower Hells Canyon/Salmon river region.

Winter Weather Advisory until 11 am MST this morning eastern

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