Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 092145
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
245 PM MST Fri Dec 9 2016

.DISCUSSION...Another weather disturbance and significant surge
of moisture will impact west central Idaho and much of western
Montana this evening, tonight, and Saturday morning. Compared to
last night, there should be more precipitation/snow. The snow will
generally occur with relatively light winds, so no blowing snow
and only moderate impacts expected. By early Saturday, the
atmosphere may become unstable enough to support organized snow
bands, especially from the Clearwaters of Idaho eastward across
the Bitterroots and southwest Montana. Under more organized snow
bands, local intense snow and very low visibility could develop.

A slightly drier air mass is expected late Saturday and Saturday
evening with a decrease in the showers.

However, another weather system and surge of moisture should shift
across north central Idaho and western Montana late Saturday night
and Sunday supporting additional snow showers and possibly a few
snow bands.

Temperatures will remain steady or slowly rise tonight...and then
moderate a little Saturday. An unstable atmosphere will move
over the area and help mix out the cold air in many valleys
(except northwest Montana where some colder air will persist).

Forecast models (namely the ECMWF) are starting to show much
better consistency through all of next week (trending towards the
GFS solution), so confidence in the weather pattern is steadily
growing. The first suit of impacts will come into play on Monday
as yet another push of relatively warm, moist air moves over the
Northern Rockies. While the snowfall is likely to start off light,
but steady, this snow will become more intense as another bout of
arctic air surges into the Northern Rockies. This next push is
quite impressive being deeper and thus spread farther west into
Alberta and British Columbia than this past arctic. This results
in gusty winds developing throughout far NW Montana (Yaak, Libby,
Troy & Eureka) nearly at the same time as these conditions develop
through the West Glacier Region and northern Flathead Valley
(US-2, Essex, West Glacier, Columbia Falls & Kalispell). Thus the
affects of blowing and drifting snow could be far more widespread
than the typical arctic intrusion and will need to be closely
monitored for winter weather highlights.

Snow will enhance throughout the day on Monday across west
central Montana and central Idaho as the arctic cold front slides
to the south. Cold air and gusty winds are likely to dump over
Evaro Hill and through Hellgate Canyon resulting in blowing and
drifting snow concerns throughout the Mission and Missoula Valleys
by Monday afternoon. By Tuesday morning the cold air will likely
have engulfed much of the Northern Rockies with wind chill
becoming quite a concern Tuesday night. Models are showing dry
air over the area on Wednesday morning and by Wednesday night the
combination of a clearing sky, calming winds and a widespread
blanket of fresh snow should lead some impressive radiational
cooling and some of the coldest temperatures we`ve seen in quite
some time.

Thereafter models are a little bit out of sync for Thursday and
Friday. So chances for light snow enter back into the forecast,
though if the ECMWF is correct there could be another potential
widespread snow event. However by next weekend there is unusually
good agreement in long range models showing even colder air
potentially taking up residence throughout the Northern Rockies.
Suffice it to say, winter is here to stay and things could turn
dangerously cold at times next week.

&&

.AVIATION...Another weather system and surge of moisture will
produce widespread snow across the northern Rockies tonight.
Mountains will become obscured and the visibility/ceilings will
become IFR many areas. Airports impacted include KMSO, KGPI,
KSMN, and KBTm.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 10 PM this evening to 11 AM MST
     Saturday Butte/Blackfoot Region.

     Winter Weather Advisory until 11 AM MST Saturday
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory from 7 PM this evening to 11 AM MST
     Saturday Missoula/Bitterroot Valleys.

     Winter Weather Advisory from 8 PM this evening to 11 AM MST
     Saturday Kootenai/Cabinet Region...Lower Clark Fork
     Region...Potomac/Seeley Lake Region...West Glacier Region.

     Winter Weather Advisory from 8 PM this evening to 11 AM MST
     Saturday Flathead/Mission Valleys.

ID...Winter Weather Advisory until 11 AM MST Saturday Eastern Lemhi
     County...Western Lemhi County.

     Winter Weather Advisory until 10 AM PST Saturday Northern
     Clearwater Mountains...Southern Clearwater Mountains.

     Winter Weather Advisory until 8 AM PST Saturday
     Orofino/Grangeville Region.

&&

$$



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