High Wind in Montana, February 1, 2020

Area Forecast Discussion
National Weather Service Missoula MT
213 PM MST Fri Jan 31 2020

...STRONG WINDS POSSIBLE SATURDAY...

.DISCUSSION...Light precipitation is starting to spread from
northwest to southeast today, with very little making it to valley
floors so far this afternoon. As the atmosphere moistens further,
precipitation reaching the ground will increase into this evening.
Rain is anticipated, however it could mix with snow at times.
Accumulations in valleys will be quite low, but snow in
mountainous terrain (roughly 5000 feet and higher) will continue
to stack up. Winds will also remain breezy through this evening in
Grangeville, ID and across the Camas Prairie, where winds have
already been gusting into the 40 mph today.

Snow will continue in the mountains on Saturday, while valleys
remain mostly dry leading up to the cold front Saturday night.
Strong winds will develop by early Saturday afternoon, becoming
stronger and more widespread through the day. Generally speaking,
southwest wind speeds of 25 to 40 mph are likely in most valley
locations, with occasional gusts to 45 mph possible in the late
afternoon and evening. Northwest Montana will have the best chance
at seeing prolonged gusty winds, particularly in higher terrain
where gusts to 65 mph will be possible (especially along the
Divide).

The cold front will slowly move southward Sunday morning, with an
area of snow extending from central Idaho to southwest Montana.
Expect a mix of rain and snow in the Bitterroot valley to turn to
all snow during the morning, with a potential for light snow
accumulations of an inch or two. The mountains can expect several
inches of new snow. The biggest impacts will occur over Lolo, Lost
Trail, and Homestake passes where 3-6 inches of snow are
expected, with the highest amounts likely over Lost Trail Pass.
Gilmore Summit in Lemhi county, ID can also expect several inches
of new snow.

Snow showers will develop behind the exiting front Sunday
afternoon. Expect a cold start to Monday with low temps in the
single digits to mid teens. By Monday afternoon, weak instability
will trigger a few snow showers over the region. Similar cold
temperatures will occur once again Tuesday morning.

The Northern Rockies will transition to a northwesterly upper
level flow by Wednesday that will last through the latter half of
the week. Models are indicating that a plume of fairly
significant moisture will be streaming into the region while under
this pattern. The mountains will have the potential of receiving
fairly steady snowfall, with the heftiest amounts being along the
Montana/Idaho border. Snow levels during this period will be
steadily rising to around 4000 feet by Thursday-Friday. The
majority of the valleys will start off as snow during this event
then transition to rain by the end of the week.

&&

.AVIATION...Southwest winds will begin to develop across
northwest Montana after 01/0600Z and strengthen as stable valley
inversions break around 01/1800Z. All terminals will experience
strong southwesterly winds thereafter, but northwest Montana will
see the longest period of winds in excess of 30 to 40 mph, with
gusts to 45-50 mph possible after 01/2200Z. KMSO, KBTM, and KSMN
will also experience a period of gusty winds around and after
01/2000Z, but speeds and duration should be less than those
expected to impact KGPI. Snow and rain will then impact terminals
after 02/0300Z. In addition, a strong upper level jet draped from
west to east across the Northern Rockies will create mountain
wave activity east of the Rocky Mountain front range.

&&

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