Winter Storm in Idaho, December 29, 2016

Area Forecast Discussion
National Weather Service Missoula MT
401 AM MST Thu Dec 29 2016

...PROLONGED COLD ARCTIC TEMPERATURES NEXT WEEK...
...SNOW EVENTS FRIDAY AND SUNDAY...

.DISCUSSION...Cloud cover is starting to spread into the region
this morning, which has been a little slower to arrive than
previous forecasts, so many valley locations have been able to get
a bit cooler than forecast. There should be enough moisture with
the disturbance associated with this cloud cover for light snow
to fall in northwest Montana during the day.

The next weather system is still on track to move
from north to south tonight through Friday. The potential for a
burst of moderate snow with the passing front is high, so quick
snow accumulations are likely to impact motorists with lowered
visibility and rapidly changing road conditions. The forecast snow
amounts of 1-3 inches in most valleys and 4-8 inches in the high
terrain and in favored locations maintains. Snow showers will
linger behind the front into Saturday, and we may be a little low
on our chances for snow in northwest Montana through Saturday
since model cross sections show enough low level moisture for snow
to continue but model precipitation outputs are all really low.

We still expect a stronger disturbance with more moisture and a
colder airmass to impact the region Saturday night and Sunday.
Forecast models continue to show north-central Idaho and west-
central Montana as the locations where the greatest snowfall
amounts will occur. Several inches of snow, even in the valleys is
a real possibility through the day on Sunday. As the low pressure
slides south and east into southern Idaho, a very cold arctic
air-mass will begin to move into western Montana from Canada. As
the leading edge of the arctic air moves through western Montana,
strong north and east winds will create blowing and drifting
snow, that will make travel very hazardous at times Sunday night
through the day on Monday. This air-mass is expected to make its
way into north-central Idaho as well, so expect another day of
blowing and drifting snow in the Camas Prairie again late Monday.

Monday night will be the start of a prolonged period of very cold
temperatures, that could have wide reaching impacts throughout
the Northern Rockies all week. Tuesday and Wednesday mornings
will likely be the coldest mornings of the week, where some
valleys along the divide could be 35 to 45 degrees below zero, and
15 to 25 degrees below zero for the Flathead valley, south
through the Missoula and Bitterroot valleys. The key word above
however; is the prolonged cold that may have the greatest
impacts. We are expecting several mornings with lows below zero
and highs during the week not getting above zero, or out of the
single digits for some. By the time the weekend comes around, is
when we could see the impacts to household pipes, pets, and
impacts to farm animals. We could also start seeing impacts from
the formation of ice jams on area rivers as well. Confidence is
high for this cold period, keep updated with the latest forecast
by monitoring our Facebook and Twitter pages and our website at
weather.gov/mso.

North-central Idaho is not expected to see quite the cold
temperatures during this time, however valleys here will also see
some mornings below zero. Some of the same impacts mentioned
above, can be anticipated here as well.

&&

.AVIATION...Much of the region is a bit cooler than forecast due
to cloud cover being slow to arrive. Latest satellite tends do
show increasing cloud cover and this trend is forecast to continue
through the morning. Model cross sections show ceilings lowering
this morning and terrain to become obscured. Snow showers are also
possible later this morning with highest chances in northwest
Montana. The next snow producing front will begin to move north to
south during Friday morning. Expect lowered ceilings and
visibilities with this front and increased winds.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&