Area Forecast Discussion
Issued by NWS Missoula, MT

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043
FXUS65 KMSO 260320
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
820 PM MST Sat Feb 25 2017

.UPDATE...Added parts of northwest Montana to the list of winter
weather advisories due to snow amounts and travel impacts
expected.


&&

.AVIATION...Expect breezy winds with some gusty conditions at all
terminals this afternoon and evening. A weather disturbance will
impact all terminals from north to south starting early Sunday
morning through Sunday night. Snow is expected to begin at KGPI
around 26/0600-1000z, KMSO between 26/0800-1200z, KBTM between
26/1600-1900z and KSMN between 26/1900-2300z. KGPI will have the
best potential for accumulations of 1"-4". Expect lowering
visibility and ceilings in addition to mountain obscurations.


&&

.PREV DISCUSSION... /ISSUED 236 PM MST Sat Feb 25 2017/

DISCUSSION...A broad trough will develop over the Western U.S.
tonight and continue through Sunday night. Within this trough a
weather disturbance will enter the Northern Rockies from British
Columbia early Sunday morning. This system will bring light to
moderate snow at times through Sunday evening. Snow accumulations
of generally 3 to 6" are expected in the mountains and lesser
amounts of 1 to 3" in valley locations. Areas in central Idaho
through Northwest Montana will have the best potential for
multiple inches of accumulating snow. Travel impacts are
anticipated over most mountain passes so Winter Weather Advisories
have been issued for early Sunday morning through the evening
hours. See the advisories for more detailed info about each
region.

The Flathead Valley may receive 1 to 3 inches of snow over a 24
to 30 hour period. Impacts should be limited especially as
afternoon temperatures in the lower 30s may hinder accumulations
on the main roads. It does look like the best potential for snow
there will be Sunday morning through the afternoon.

As the trough axis moves overhead Sunday night into Monday, snow
showers will continue across the area. Afternoon temperatures near
freezing Monday will likely cause some melt of new snow,
minimizing accumulations in valleys, but expect the passes to
remain snowing and snow covered into Tuesday.

Tuesday through Thursday, a transition to a moist northwest flow
pattern will allow scattered snow showers to continue. Although
temperatures remain cold enough to keep snow for elevations above
above 2000 feet, periods of sun during the day will cause melting
on surfaces, especially given the isolated, convective nature of
the showers. So overnight refreeze of moisture on roadways could
cause patchy black ice.

Next weekend, models show a strong cold front moving through ahead
of a longwave trough. Strong valley winds gusting to 30+ mph would
likely accompany this front as it moves through. The exact timing
of the frontal passage varies from model to model, but Saturday
currently looks the most favorable. Widespread precipitation would
also be associated with the feature, with rain transitioning to
snow as the front moves past.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 5 AM to 11 PM MST Sunday
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory from 2 AM to 11 PM MST Sunday
     Flathead/Mission Valleys.

     Winter Weather Advisory from 2 AM to 11 PM MST Sunday West
     Glacier Region.

     Winter Weather Advisory from 2 AM to 11 PM MST Sunday
     Kootenai/Cabinet Region.

     Winter Weather Advisory from 2 AM to 11 PM MST Sunday for I-90
     Lookout Pass to Haugan in the Lower Clark Fork Region.

ID...Winter Weather Advisory from 4 AM to 10 PM PST Sunday Lower
     Hells Canyon/Salmon River Region...Orofino/Grangeville
     Region.

     Winter Weather Advisory from 4 AM to 10 PM PST Sunday Southern
     Clearwater Mountains.

     Winter Weather Advisory from 4 AM to 10 PM PST Sunday Northern
     Clearwater Mountains.

&&

$$



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