Area Forecast Discussion
Issued by NWS Missoula, MT

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000
FXUS65 KMSO 311013
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
411 AM MDT FRI OCT 31 2014

...SIGNIFICANT MOUNTAIN SNOWS ABOVE 4500 FEET THIS WEEKEND...

.DISCUSSION...The lowest parts of the atmosphere remain quite
saturated across the area this morning and thus fog and low
clouds are expected to persist through much of the morning. Some
reductions in visibility will be possible during the morning
commute so please plan accordingly.

The well-advertised upcoming storm system can be seen well off
the West Coast this morning. Over the next twenty-four hours it
is forecast to move inland and across northern California into
northern Nevada. But beyond this point the track starts to become
less certain. The NAM and ECMWF both continue to trend westward
with the upper-level features and attendant heavy precipitation.
This westerly track is also concerning since the models are
subsequently bringing additional warm air into southwest Montana
late Saturday afternoon, effectively keeping the snow level higher
than previously forecast.

Meanwhile, the GFS model is showing a weaker, faster moving
storm (though with less of a westerly jog). It also appears to
bring in more warm air Saturday afternoon into the early evening
hours. Considering this agreement of the models, we have decided
to start the Winter Storm Watch at 00z Sunday and have changed it
to be for locations above 4500ft (which was where the previously
issued watch was already focused).

We have also adjusted the heaviest precipitation to be focused a
bit more into west central Montana and along the Idaho/Montana
border in accordance with the model trends. There is high
confidence that snow will significantly impact travel on Lost
Trail, Bannock, Lemhi and Lolo Pass. However confidence is a bit
lower for Homestake and MacDonald Pass. Regardless of model,
significant high mountain (above pass level) snow is still
expected to pose a significant hazard to hunters and
recreationists in the Bitterroot, Sapphire, Anaconda, Flint
Creek, Mission and Swan Mountain Ranges.

Heavier snow will quickly turn to lighter snow showers as this
winter system moves east. Most of the precipitation will diminish
Sunday evening as a weak ridge builds over the region through
Monday.

Next week will remain fairly cool, cloudy, and rainy at times as the
Northern Rockies remains in a generally steady stream of moisture
moving inland from the Pacific Ocean. While not every day is
expected to be dreary, rainfall will be more common than sunshine,
especially across NW Montana. Locations in south central Idaho
such as Salmon and Leadore meanwhile will have a much lesser
chance of precipitation. Snow levels look to be generally higher
than this weekend`s storm, near pass level early in the week, then
rising above passes by later in the week.

&&

.AVIATION...Moist low-level conditions in the valleys will lead
to patchy fog and low clouds this morning, causing reduced
visibilities and periodic low ceilings at KGPI and KMSO.
Conditions will begin to improve by mid-morning. Elsewhere,
partly cloudy skies and light winds will continue. Light rain
will be on the increase across far northwest Montana and north-
central Idaho by this evening ahead of a winter storm arriving for
the weekend.



&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WATCH from Saturday evening through Sunday
     afternoon ABOVE 4500 FEET for the Bitterroot/Sapphire
     Mountains...Butte/Blackfoot Region...Potomac/Seeley Lake
     Region...West Glacier Region.

ID...WINTER STORM WATCH from Saturday evening through Sunday
     afternoon ABOVE 4500 FEET for the Eastern Lemhi County...
     Southern Clearwater Mountains...Western Lemhi County.

&&

$$




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