Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 202156

Area Forecast Discussion
National Weather Service Missoula MT
256 PM MST Mon Feb 20 2017


Periodic mountain snow and valley snow/rain shower activity will
be present over the Northern Rockies through Wednesday. Snow
levels will generally be greater than 4000 feet during this time;
however, a few intense showers may allow snow to accumulate
briefly on the valley floors. Sudden reduced visibility combined
with light, brief snow accumulations will create highly variable
and potentially hazardous conditions. Roads will frequently
become slick over area mountain passes. Also, during each
afternoon through Wednesday, there is a slight chance that
isolated lightning strikes will develop during the peak of
afternoon shower activity.

Thursday through Saturday, a somewhat drier and cold airmass will
exist over the Northern Rockies. Temperatures will be noticeably
colder over the region during this time. Despite the relatively
dryness of the airmass, the cold air aloft will allow snow shower
activity to exist each day. Snow accumulations will be largely
minor and most pronounced over the high terrain and mountain
passes. There is a chance of scattered slick conditions at valley
elevations each morning; however, snow accumulations will be

Sunday through Monday, models suggest that a modified arctic
airmass will move along the Continental Divide. It is unclear
whether a significant cooldown will occur on the west side of the
Divide (western Montana), however this scenario will reinforce
relatively cold air already in-place over the region. This arctic
airmass will need to be watched closely, as it has some features
in common with the notorious February 2014 blizzard event that
occurred in the Missoula Valley. Stay tuned.


.AVIATION...Rain and snow showers will continue to impact aviation
this afternoon and evening. Daytime heating decreases after
21/0000z, after which many sites will likely switch from rain to
snow or melting snow in the layer closest to the ground, which
may reduce visibility further during periods of precipitation.
Shower activity decreases after 21/0600z, but fog and low cloud
decks remain, especially in northwest Montana and KGPI. South and
southwest wind gusts to 25 kts should be expected at KSMN and KBTM
through sunset, but models indicate lingering convective shower
activity could cause occasional 20 to 30 kt gusts overnight as
well, as evaporating showers bring winds down to the surface.



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