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000
FXUS65 KMSO 011155
AFDMSO

AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
454 AM MST SUN FEB 1 2015

...Winter weather and slick roads to return this afternoon and
evening...

.DISCUSSION...A weather disturbance will begin to spread
precipitation into north central Idaho later this morning, and
into western Montana by this afternoon. Most locations will start
off cold enough to receive mainly snow, however initial amounts
should be relatively light. Precipitation will begin to intensify
this evening with the approach of the upper level jet stream,
especially in the higher terrain. Downsloping effects for the
larger valleys are expected to begin due to increasing winds
aloft tonight, particularly for valleys along and south of the
Interstate 90 Corridor. Across northwest Montana, downsloping
effects are not expected to be as pronounced. Therefore, numerous
winter weather advisories have been issued due expected slick,
snow covered roads. It is possible these advisories will need to
be extended into the Flathead/Mission valleys and possibly for
Whitebird Grade in Idaho.

Precipitation will gradually taper off for the valleys by Monday
morning, with light snow continuing in the higher terrain. A brief
period of freezing drizzle is possible for northwestern Montana
valleys Monday morning as drier air works into the snow production
zones aloft, although confidence in this occurring is fairly low
at this time.

An upper level disturbance will bring an increasing chance for
precipitation by Monday evening. Many valley locations across
central Idaho and southwest Montana will be able to warm between 4
to 7 degrees above normal for high temperatures. Other locations
with persisting cold pools like Salmon, Idaho or across the
Flathead Valley will struggle to warm up.
 * More snow is expected for mountain passes including Lookout,
   Lolo and Marias...amounts ranging from 3 to 6 inches through
   Tuesday morning.
 * Another potential impact will be valley locations that are able
   to cool down into the lower 30s Monday night allowing for black
   ice and slick conditions for untreated surfaces.

Tuesday: Relatively moist west-northwest flow will support light
mountain snow and the chance for rain/snow mixture or rain in the
valleys. There is still a question how far west the arctic air on
the east side of the Continental Divide will penetrate. There
continues to be the potential for Marias Pass to West Glacier to
see the colder air, but even could make it into the Flathead
Valley by Tuesday night. Snow and slick conditions would ensue if
this were to happen there.

Tuesday after 5 pm MST/ 4pm PST: Yet another moist weather
disturbance will move into the region especially across central
Idaho, Lemhi County into southwest Montana. With the timing of
this moisture influx, places like White Bird Grade south of
Grangeville, Elk City, Dixie to Lost Trail Pass and perhaps
portions of northern Lemhi County could see a period of snowfall.
Models are hinting at the arctic cold frontal boundary stalling
out across southwest Montana and this could pose a problem for the
I-90 corridor east of Missoula, Georgetown Lake area to Butte with
snow.

Wednesday: There are discrepancies on what may transpire, so
confidence is low, but at this point expect possible showers
across northwest Montana and the chance for continued rain/snow
across central Idaho to Lemhi County.

A warm and moist system with subtropical origins is possible
Friday into the weekend. This could bring significant
precipitation, especially for the mountains, and well above normal
temperatures for much of the region. Due to rising snow levels
and potential for heavy rain, there could be an increased risk
of rock/mud slides and ponding of water in valley locations, especially
in north central Idaho and northwest Montana. Stay tuned for
further details.

&&

.AVIATION...A weather system will move in to north central Idaho
this morning, and into western Montana this afternoon. This will
allow for lowering ceilings which will obscure the higher terrain
across the region. Light to moderate snow is expected to develop
by this afternoon, which will impact the higher terrain across all
of the region and valleys across northwest Montana. Airfield
KGPI is the most likely to be impacted by accumulation snow.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY from 11 AM this morning to 9 AM MST
 Monday Bitterroot/Sapphire Mountains...Lower Clark Fork Region.

     WINTER WEATHER ADVISORY from 2 PM this afternoon to 9 AM MST
     Monday Potomac/Seeley Lake Region...West Glacier Region.

     WINTER WEATHER ADVISORY from 11 AM this morning to 9 AM MST
     Monday Kootenai/Cabinet Region.

ID...WINTER WEATHER ADVISORY from 10 AM this morning to 8 AM PST
     Monday ABOVE 3000 FEET for the Northern Clearwater
     Mountains...Southern Clearwater Mountains.

&&

$$