Winter Storm in Montana, January 18, 2017

Area Forecast Discussion
National Weather Service Missoula MT
358 AM MST Wed Jan 18 2017

...Snow, sleet and freezing rain expected today...

.DISCUSSION...The first initial slug of moisture has made its way
across northern Idaho into northwest Montana this morning. It
appears that the precip. type is mainly snow, especially at
Lookout Pass where moderate snow has been occurring for a few
hours now. It's hard to tell, but it appears that there may be
rain falling at Greer Grade in Clearwater County Idaho. While the
precip. type may change back and forth this morning, the impacts
will continue to be the same: a sloppy morning commute expected.

Idaho:
There is some indication that the snow levels by Pierce, Elk River
and towards Orofino may lower a little bit this morning along with
heavy precipitation. As a result, a few areas could see a period
of very heavy wet snow which could cause some strain on power line
infrastructure and intermittent power outages. Whitebird Grade is
expected to experience snow and eventually a mixture with sleet or
freezing rain by mid morning. Also areas south of Riggins towards
the county line may see a wintry mixture this morning. So
therefore we are issuing a winter weather advisory for those
locations. The cold air seems to be quite deep across Lemhi County
which will cause the precip type to be more snow. They could see a
mix with sleet this afternoon. Although the heaviest precipitation
is expected to occur over north-central Idaho today, lingering
rain, freezing rain or snow is expected through Thursday morning.

Montana:
Quite a complex weather scenario for western Montana. Higher
elevation locations this morning are in the 30s and 40s while
dewpoints remain in the teens. Valley locations range from the
single digits to 40s(Philipsburg). An example of extreme
temperature difference is 7 degrees in Butte while it's 34 degrees
at the Anaconda Airport. At this point, it appears that the precip
type will begin more as snow or a snow/sleet mixture. Stations
upstream including Sandpoint, Idaho have been mainly snow. By
daybreak or after daybreak, there may be enough milder air pushing
into the region that some locations will see freezing rain mixing
in. Hamilton may be the first location in the Bitterroot Valley to
jump up towards or eclipse the freezing mark by this afternoon
while Missoula may stay in the 20s. Once this plume of moisture
transitions southward by this afternoon, precipitation intensity
will decrease somewhat, but the threat for a mixture of freezing
rain and sleet will continue through Thursday morning.

Snow showers continue into Friday with a decreasing trend through
the day. Temperatures are also anticipated to return to just
below normal through the weekend with snow showers possible.

The Sunday into Monday weather system is still on track to bring
high chances for snow with showers to linger into Tuesday. A drier
upper ridge may return on Wednesday so watch out for the return of
cold valley inversions.

&&

.AVIATION...The complex weather situation is evolving early this
morning as warm air moves in aloft and cold air is trapped in most
valleys. There has been a wide range of precipitation types from
rain, freezing rain, to light and moderate snow overnight in
eastern Washington through north central/northern Idaho. As the
main moisture tap moves east and into western Montana
precipitation will begin to fall during this morning. The
temperature and moisture profile from model soundings now look
more favorable for inverted valleys to start with snow, but
freezing rain and sleet will both be possible through today.
Valley locations that are able to warm will also have gusty south
winds, which will primarily be from Grangeville through
Philipsburg and Anaconda. The threat for icing and freezing rain
will extend into Thursday morning.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 11 PM MST this evening
     Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region...
     West Glacier Region.

     Winter Weather Advisory until 11 PM MST this evening
     Flathead/Mission Valleys.

     Winter Storm Warning until 11 PM MST this evening
     Kootenai/Cabinet Region.

     Winter Storm Warning until 11 PM MST this evening Lower Clark
     Fork Region.

ID...Winter Weather Advisory until 10 PM PST this evening Lower Hells
     Canyon/Salmon River Region.

     Winter Storm Warning until 10 PM PST this evening Northern
     Clearwater Mountains...Orofino/Grangeville Region.

     Winter Weather Advisory until 10 PM PST this evening Southern
     Clearwater Mountains.

&&