Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 132125

Area Forecast Discussion
National Weather Service Missoula MT
225 PM MST Wed Dec 13 2017

.DISCUSSION...High pressure will build over the region tonight and
persist through Thursday night. This should translate into dry
conditions, but increasing areas of valley fog and low stratus
again from Orofino and Grangeville eastward across western Montana
and Lemhi County. In addition, the light snow that occurred
Wednesday will translate in persistent local slick roads,
especially across southwest Montana and Lemhi County.

The next weather system is due into the area late Friday into
Saturday. Cold air will remain trapped in many of the valleys as
this system begins to spread moisture into the region...but the
cold valley air should eventually be mixed out as the atmosphere
becomes unstable Friday night and Saturday. As such, the
precipitation should start as snow in many areas...possibly
transitioning to mixed rain/snow Friday evening...before going
back to snow by Saturday morning. The mixed wintry precipitation
should only be on the light to moderate side and mostly focused
over north-central Idaho (Orofino eastward across Clearwaters)
and the higher terrain of western Montana. Lookout, Lolo, Marias,
and Lost Trail Passes should become snow bound again.

A cooler and drier air mass will be over the region Saturday
night and Sunday.

There is quite a bit of forecast uncertainty for next week.
However, it appears a moist northwest flow may set up mainly over
northwest Montana Monday and Tuesday with generally dry conditions
Lemhi County and southwest Montana. The air mass will only be
marginally cool, so mixed precipitation (snow, rain and possibly
local freezing rain) appears to be the main threat.

In the longer term, models continue to shift back and forth from a
cooler/moist trough of low pressure to a cold arctic system.
Uncertainty is very high...but additional precipitation seems


.AVIATION...Significant moisture will persist in the low levels of
north central Idaho, Lemhi County and western Montana. Drying
aloft will support enough cooling to allow areas of fog and
stratus to develop in most valleys tonight into Thursday morning.


MT...Winter Weather Advisory until 8 PM MST this evening
     Butte/Blackfoot Region.


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