Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 290450
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
950 PM MST FRI NOV 28 2014

.UPDATE...Cancelled the Wind Advisory early and updated timing of
the approaching arctic air mass.

&&

.DISCUSSION...First things first, have decided to cancel the wind
advisory for the Grangeville area early. Conditions which help
enhance the wind are quickly diminishing, but breezy conditions
with frequent gusts to 30 mph through the night.

Have been watching the approaching arctic and it appears to be
moving faster than previously forecast. This was handled
reasonablywell by the latest NAM model, so leaned on it for
forecast snow level overnight. The arctic has moved through
Glacier National Park and will be blasting out of Bad Rock Canyon
anytime now. Meanwhile north of the border the arctic has plunged
over the Divide and is filtering its way down the Lake Koocanusa
valley towards Eureka. It is also filtering down the Moyie River
valley towards the Idaho Panhandle and far northwest Montana. The
cold air should arrive in Eureka by midnight and northwest
Montana (Yaak area) by 3am at the latest, quickly turning steady
rain into snow. Timing of the arctic into Missoula and similar
southern points has changed little, however, with it reaching by
Saturday afternoon.

&&

.AVIATION...Light rain today will transition to heavy mountain
snow and moderate to heavy valley snow starting around 29/0300Z.
Gusty winds up to 35 to 40 kts are likely at KGPI around this same
time frame and will last through Saturday morning, in addition to
low visibility and ceilings due to snow and blowing snow. All
other terminals will experience impacts to aviation due to
snowfall and gusty winds, but snowfall is not expected to be as
great in these areas. Periods of intense snowfall are still
likely, with intermittent ceiling/vis reductions. Expect inclement
conditions to affect the Northern Rockies through the day Saturday
before conditions start to finally ease up.


&&

.PREV DISCUSSION... /ISSUED 150 PM MST FRI NOV 28 2014/

..ARCTIC FRONT TO IMPACT NORTHERN ROCKIES TONIGHT THROUGH
SATURDAY...
..BITTERLY COLD TEMPERATURES BY SUNDAY...

DISCUSSION...With the arctic front now past the Canadian/US
border east of the Divide, it won`t be long until the harsh
effects of the front will begin to impact western Montana and
central Idaho. Given the high confidence in this front and all of
its associated impacts tonight and through the weekend, various
winter storm warnings/advisories have been issued.

The main impacts still remain as follows:

1) SNOW AND BLOWING SNOW CAUSING INCLEMENT TRAVEL: Northwest
Montana will be hardest hit tonight into Saturday as far as
snowfall and gusty east winds are concerned. Locations along
Highway 93 from Eureka south and east to the Divide will be most
impacted, with travel expected to be nasty over Marias Pass due to
intense snow/blowing snow. Any wet roads caused by rainfall today
could flash freeze, creating an icy surface for snow to fall on,
exacerbating travel issues through Saturday morning.

Snow across west central Montana and north central Idaho will also
present travel problems, especially over mountain passes
connecting the Idaho/Montana border. Accumulations over passes
will be greater than in valleys, where roads may become difficult
for a time but aren`t expected to last as long as across NW MT.
Those traveling over Lookout and Lolo passes will encounter very
snowy travel, so plan accordingly.

2) BITTERLY COLD TEMPS/WIND CHILLS: Behind the arctic front,
expect winds to remain elevated as the coldest air settles over
the region. Temps have been mild recently, remaining in the 40s
and 50s, but will crash into the single digits and teens by
Sunday. This will definitely be felt, especially Sunday and
Monday mornings when temps will be in the single digits. Wind
chills in the negatives should be anticipated during this time.

Next week will feature a slow warming trend to near normal
temperatures by mid-week. a series of weak weather systems will
spread a chance of light precipitation across the area.

AVIATION...Light rain today will transition to heavy mountain
snow and moderate to heavy valley snow starting around 29/0300Z.
Gusty winds up to 35 to 40 kts are likely at KGPI around this same
time frame and will last through Saturday morning, in addition to
low visibility and ceilings due to snow and blowing snow. All
other terminals will experience impacts to aviation due to
snowfall and gusty winds, but snowfall is not expected to be as
great in these areas. Periods of intense snowfall are still
likely, with intermittent ceiling/vis reductions. Expect inclement
conditions to affect the Northern Rockies through the day Saturday
before conditions start to finally ease up.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...     WINTER WEATHER ADVISORY until 11 AM MST Saturday
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
     Kootenai/Cabinet Region...Lower Clark Fork Region...
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region.

     WINTER STORM WARNING until 11 AM MST Saturday Flathead/Mission
     Valleys...West Glacier Region.

ID...     WINTER WEATHER ADVISORY until 10 AM PST Saturday Northern
     Clearwater Mountains...Southern Clearwater Mountains.

&&

$$



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