Winter Weather Advisory 13, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
349 AM MST Tue Feb 7 2017

.DISCUSSION...Scattered snow showers and snow bands continue to
produce quick bursts of light to moderate snow for isolated areas
around western Montana this morning. Due to this and from the
refreeze of melting snow yesterday afternoon, Winter Weather
Advisories remain in place until 11am this morning. They very well
could be allowed to expire before then, after the morning
commute.

Our next weather system will begin to impact portions of the
Northern Rockies this afternoon and evening, extending into
Wednesday morning. A weak warm front will move north from
southern Idaho into west-central Montana and north-central Idaho,
overrunning much cooler air at the surface. This scenario usually
produces widespread areas of light to moderate snow. The front
will have problems making it much farther north than the Mission
Valley in Montana, and to the border with Clearwater and Shoshone
Counties in Idaho. Only modest accumulations of 3 to 7 inches of
snow is expected for north-central Idaho. Areas such as Elk River,
Pierce, Grangeville region, and Lowell will be on the lower
range, while Elk City and Dixie being on the upper end. The
Missoula/Bitterroot Valley and points south through SW Montana and
Lemhi Co will see lighter accumulations of 1 to 3 inches.

A much stronger and wetter system is still on track to impact much
of the Northern Rockies on Thursday. The difference with this
storm, compared to recent storms, is that warmer air will be
associated with it. So most valleys will see more rain than snow,
with the exception of northwestern Montana, where the colder air
will likely hold on longer than most areas. Locations such as
Troy, Yaak, and Libby, just to name a few, could see significant
impacts due to more heavy wet snow on top of what was just
received. These areas could see another 6 to 12 inches of snow
that will add a significant amount of weight on area roofs. Once
the warmer air finally takes over, some of these locations could
see an additional .50 inch or more of rain, that will exacerbate
snow loading impacts. Areas farther east such as Kalispell to
West Glacier will experience similar impacts, with slightly lower
snow amounts before turning to rain.

For locations farther south, in west-central Montana and central
Idaho, Snow will turn to rain much sooner, so impacts due to
accumulating snow will not be the biggest impacts. It will be rain
on top of snow melt, that could lead to localized minor flooding
around homes and poor drainage areas. A significant amount of
ponding can be expected through the day on Thursday. Also, light
freezing rain could occur for a brief period of time Thursday
morning in western Montana valleys. Snow-levels will be at their
highest point of 5000-6000 feet, early Thursday evening.

Cold air will begin ushering into the area by Friday morning,
helping to lower snow levels back to valley floors for much of
western Montana and parts of north-central Idaho. Snow showers
will linger throughout the day Friday in the wake of the colder
air mass, with the MT/ID border and northwest Montana remaining
the most active. Shower activity will decrease a bit throughout
the day Friday, but this won't last long as a cold shortwave
trough tracks down into the northern Rockies by Friday night/early
Saturday morning. Another round of moderate snowfall can be
expected during this period as this feature makes its way through
the Northern Rockies. This additional snow will add to the
overwhelming snow depth already present across northwest Montana.

By Sunday into early next week, a warm and dry high pressure will
move over the Pacific Northwest. Temperatures will be slow to
modify where snow cover and valley inversions are present, but
the warm air mass will support snow melt and aid in sloppy road
conditions for locations that warm near to above freezing.

&&

.AVIATION...Snow showers are lingering in west-central and
northwest Montana this morning in the vicinities of KMSO, KGPI,
and KBTM. Showers that do move over the terminals will be short
lived, but could produce brief periods of lower visibilities and
ceilings. Showers with this system will be diminishing after
07/1400Z, but a strong surface pressure gradient with breezy winds
will remain over the Continental Divide through today.

After 07/1800Z, a warm front will move northward into north-
central Idaho and bring light to moderate snow to KSMN. KBTM and
KMSO will also see snow later this afternoon as the front slowly
propagates northward today.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 11 AM MST this morning
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
     Missoula/Bitterroot Valleys.

     Winter Weather Advisory until 11 AM MST this morning Lower Clark
     Fork Region...Potomac/Seeley Lake Region.

     Winter Weather Advisory until 11 AM MST this morning
     Flathead/Mission Valleys...Kootenai/Cabinet Region.

     Winter Weather Advisory until 11 AM MST this morning West
     Glacier Region.

ID...None.
&&

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
803 AM MST TUE FEB 7 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0500 AM     SNOW             1 NNW BIGFORK           48.08N 114.08W
02/07/2017  M2.5 INCH        FLATHEAD           MT   COCORAHS

            COCORAHS STATION BIGFORK /MT-FH-27/.

&&

NWS MISSOULA MT
IRIS SYSTEM