Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 252158
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
257 PM MST TUE NOV 25 2014

.DISCUSSION...
Moderate to heavy precipitation is anticipated to continue and
even intensify across north-central Idaho and southwest/west-
central Montana this afternoon and evening. Meanwhile, a weak
surface low currently near Walla Walla WA is forecast to drift
eastward along a track just south of the Bitterroot Valley,
effectively drawing colder air currently over far NW Montana as
far south as Missoula and the I-90 corridor. Then, into the
overnight hours, snow levels are expected to rise quickly from
southwest to northeast across central Idaho and western Montana as
warmer air moves in. This all makes for a rather complicated
precipitation-type forecast for the valleys. In general, snow is
expected from around Missoula northward tonight, eventually
switching over to rain by daybreak (Kalispell area could stay as
snow until noon tomorrow). The passes will see snow and dangerous
driving conditions through early Wednesday, with passes under
7000` changing over to a slushy mix.

By mid-day Wednesday, precipitation will mostly be limited to
showers across northwest Montana. Snow levels will continue to
rise above all valley locations by the afternoon. Travel impacts
due to snow should mainly be isolated to the highest passes such
as Lost Trail and perhaps Homestake.

Thanksgiving day looks to be the most mild day of the week with
mainly scattered showers across northwest Montana. Western Montana
and north central Idaho could see a few showers as well but it
should mainly be over higher terrain. High temperatures are expected
to be in the low to mid 40s.

The models are in fairly good agreement of an arctic moving into
the Northern Rockies Friday night into Saturday. Ahead of the
arctic, a plume of moisture will stream into the region causing
widespread precipitation. The snow levels will be fairly high with
the onset of precipitation so most valley locations will receive
rain, while the higher terrain will receive significant snow. The
arctic is currently advertised as moving into northwest Montana
Friday night causing snow levels to crash to the valley floor. The
interaction of the arctic with the moisture plume could enhance
the snow across this region. Currently, the valleys across
northwest Montana including Flathead and Mission valleys are
expected to receive 2 to 6 inches of snow by Saturday Morning. The
arctic will continue to push across the Northern Rockies on
Saturday with the heaviest snow being along the leading edge of
the front. North central Idaho into west central Montana should
receive 2 to 5 inches of snow during the day on Saturday. The
quick change from rain to snow to very cold temperatures could
create a flash freeze situation and thus very difficult driving
conditions across the region during this holiday weekend. The
easterly winds associated with this arctic could cause significant
winds chill values especially during the day on Saturday.

The system will clear out Saturday night allowing temperatures to
drop into the single digits and below zero for many areas across
western Montana. While Idaho temperatures will primarily be in the
20s and 30s.

The models are indicating a low pressure system lifting into
region from northern California Sunday night into Monday which
should help scour out the arctic air. This system will bring some
scattered showers and warmer temperatures.

&&

.AVIATION...Precipitation at KMSO, KBTM and KSMN is expected to
continue through tonight and into early Wednesday morning. KMSO is
currently raining but it it expected to transition into snow
around 25/2300Z and then back to rain early Wednesday. KBTM will
continue to see moderate snow through this afternoon before
becoming lighter tonight. KGPI should see increasing precipitation this
afternoon and overnight with periods of moderate snow. Main
impacts at area terminals will be reduced visibilities, low
ceilings, and mountain obscurations. Rain/snow will be decreasing
throughout the day Wednesday with the heaviest prcepitation during
the morning.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY until 5 AM MST Wednesday
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region.

     WINTER WEATHER ADVISORY until 5 AM MST Wednesday
     Missoula/Bitterroot Valleys.

     WINTER WEATHER ADVISORY until 5 AM MST Wednesday Lower Clark
     Fork Region.

     WINTER WEATHER ADVISORY until 11 AM MST Wednesday
     Flathead/Mission Valleys...Kootenai/Cabinet Region.

     WINTER STORM WARNING until 11 PM MST Wednesday West Glacier
     Region.

     WINTER STORM WARNING until 11 AM MST Wednesday Potomac/Seeley
     Lake Region.

ID...WINTER WEATHER ADVISORY until 11 PM MST this evening for Lost
     Trail Pass in the Eastern Lemhi County.

     WINTER WEATHER ADVISORY until 10 PM PST this evening ABOVE 4000
     FEET for the Northern Clearwater Mountains...Southern
     Clearwater Mountains.

     WINTER WEATHER ADVISORY until 11 PM MST this evening ABOVE 5000
     FEET for the Western Lemhi County.

&&

$$



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