Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 132155

Area Forecast Discussion
National Weather Service Missoula MT
255 PM MST SAT FEB 13 2016

.DISCUSSION...Showers continue to linger across western Montana
and central Idaho this afternoon. These showers are resulting in
mainly a mix of rain/snow and graupel, with little impact to
roadways. Shower activity will likely decrease this evening ahead
of the next weather system.

Another weather system will begin to move into the region late
this evening into Sunday. This weather disturbance has more
moisture associated with it than the system that brought rain and
snow last night into this morning. Snow levels will initially be
starting out at around 3500 feet, slowly increasing to around 5000
to 6000 feet by Sunday afternoon. This will result in accumulating
snow for elevations generally above 4000 feet, primarily impacting
area mountain passes. Valleys will likely also see some light snow
initially, however this should change over to a mix of rain and
snow by mid day Sunday. With road surfaces remaining quite warm,
impacts to valley roadways are expected to be brief, if at all.
Winter weather advisories have been issued for the mountain passes
to address slick roadways and potentially slow travel tonight
through Sunday morning.

Starting late Sunday, a plume of moisture originating from the
tropics will bring moderate to heavy rainfall and rising snow
levels through Monday. The areas expected to see the greatest
moisture will be over the mountains of north central Idaho and
parts of northwest Montana. Rainfall amounts of 1 to 2 inches are
expected with locally up to 3 inches over the Clearwater
Mountains of Idaho. A Hydrologic Outlook was issued for the
increasing threat of rock and mud slides especially over prone
areas such as highway 12 in Idaho and Interstate 90 near Lookout
pass. For valleys, periods of moderate rain will lead to ponding
of water on area roadways. In areas with snow on the ground, warm
temperatures and breezy winds on Monday will lead to rapid snow
melt and could cause further ponding of water issues.

By late Monday into Tuesday, the moisture plume is expected to
move further north into northwest Montana. There is still
uncertainty on how much moisture will be left, with one model
still showing moderate precipitation over the area and the other
showing mainly light precipitation. By late Tuesday, a dirty ridge
of high pressure will begin to build over the area. Clouds and
light precip is likely to linger across the region through

There continues to be agreement that another trough will move into
the region around the Thursday Friday time-frame of next week.
Snow levels look to be fairly high as the trough moves into the
region and will lower with a cold front. High pressure will likely
briefly arrive after this trough, but there are indications that
additional weak shortwaves will pass through the weekend. There is
low confidence in the forecast after the Thursday-Friday trough.


.AVIATION...Showery conditions will continue to affect western
Montana and central Idaho with spotty areas of lowered ceilings
and visibility. Precipitation has been falling in the form of a
mix of rain, snow and graupel and will have the potential to
affect all airfields through 14/0100z. The next weather system
will begin to move into central Idaho and northwest Montana late
this evening, spreading into west central and southwest Montana
tonight into Sunday morning. Precipitation will primarily fall as
snow at all elevations initially, changing over to valley rain
during the day Sunday. Widespread obscurations of the terrain
should be expected due to low ceilings. Airfields KMSO, KSMN, KGPI
and KBTM may see brief visibility reductions due to snow by early
Sunday morning, but these should be fairly short lived. In
addition, winds will become gusty from the west on ridge tops
early Sunday morning, up to about 45kts. Some of this wind will
translate down into the valleys of southwest Montana by mid day
Sunday, possibly impacting KBTM with wind gusts near 25 kts.


MT...Winter Weather Advisory from 5 AM to 3 PM MST Sunday
     Butte/Blackfoot Region.

     Winter Weather Advisory from 11 PM this evening to noon MST
     Sunday ABOVE 4000 FEET for the Bitterroot/Sapphire

     Winter Weather Advisory from 9 PM this evening to noon MST
     Sunday ABOVE 4000 FEET for the Lower Clark Fork Region.

     Winter Weather Advisory from 11 PM this evening to noon MST
     Sunday ABOVE 4000 FEET for the West Glacier Region.

ID...Winter Weather Advisory from 10 PM this evening to 11 AM PST
     Sunday ABOVE 4000 FEET for the Southern Clearwater


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