Special Weather Statement, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
147 PM MST Thu Jan 21 2021

.DISCUSSION...Regional radar and satellite imagery show an area
of light snow across eastern Washington, northeast Oregon, and
north central Idaho this afternoon. Warm surface temperatures
(32-34F) have limited accumulations on area roadways so far this
afternoon. Light snow will spread across west central Montana and
Lemhi County Idaho later this afternoon and evening. The afternoon
and evening commute will need to be closely monitored as
temperatures fall below freezing this evening. If snow is able to
accumulate on roadways, slick travel conditions could occur. Light
snow will continue into Friday morning as a surface low moves
into central Idaho. The majority of locations south of the I-90
corridor will see accumulations of up to one inch. Isolated
snowfall amounts up to 3 inches can not be ruled out, given that
light flow events such as today have shown a history of producing
snowfall amounts higher than model guidance typically suggests.
Nonetheless, 3 inches or more of snowfall remains a low
probability outcome for most locations.

Cold seasonable temperatures are expected this weekend. High
temperatures will reach into the upper 20s to low 30s. Low
temperatures Sunday morning will drop into the single digits to
low teens across western Montana. Areas along the Divide and
across Lemhi County Idaho could drop well below zero if skies
clear out and fresh valley snow cover is present Sunday morning.

Sunday into Monday, an upper level trough will dig south along
the Pacific Northwest coast and will split apart as it moves into
California. This system could produce another round of light
snowfall, particularly along the Idaho and Montana border.

Model ensemble guidance continues to suggest a deep upper level
low will dig southward along the British Columbia and Pacific
Northwest coast Tuesday into Wednesday. This pattern will place
the Northern Rockies under a southwesterly flow. Periodic impulses
of moisture will lead to light snowfall events Tuesday and
Wednesday next week. These light snowfall events remain difficult
to predict and will need to be closely monitored in the days to
come.

&&

.AVIATION...Regional radar and satellite imagery show an area of
light snow across eastern Washington, northeast Oregon, and north
central Idaho this afternoon. Light snow is expected to bring
visibility reductions across west central Montana and Lemhi County
Idaho between 21/2200Z and 22/0600Z. Most locations south of the
I-90 corridor will see accumulations of around one inch. There is
a low probability of isolated amounts of up to three inches,
including KSMN and KBTM. IFR to MVFR stratus will linger through
at least 22/1800Z as the storm system begins to depart the region.

&&

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

Special Weather Statement
National Weather Service Missoula MT
752 PM MST Thu Jan 21 2021

IDZ005-006-MTZ004>007-043-220330-
Southern Clearwater Mountains ID-Northern Clearwater Mountains ID-
Bitterroot/Sapphire Mountains MT-Missoula/Bitterroot Valleys MT-
Lower Clark Fork Region MT-Butte/Blackfoot Region MT-
Potomac/Seeley Lake Region MT-
752 PM MST Thu Jan 21 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN IDAHO...EAST CENTRAL
CLEARWATER...SOUTHEASTERN MINERAL...SOUTHERN MISSOULA AND NORTH
CENTRAL GRANITE COUNTIES UNTIL 830 PM MST/730 PM PST/...

At 748 PM MST/648 PM PST/, Doppler radar was tracking a line of snow
showers along a line extending from Alberton to Bonner-West
Riverside. Movement was southeast at 15 mph.  Brief reductions in
visibility and quickly changing road condition is a short period of
time is possible.  Highway 93 and highway 12 between Missoula and
Florence, as well as Interstate 90 from Missoula to Bearmouth will
be impacting the greatest.

Locations impacted include...
Missoula, Lolo, Nimrod, Lolo Hot Springs and Clinton.

LAT...LON 4666 11457 4666 11338 4683 11344 4679 11475
TIME...MOT...LOC 0248Z 331DEG 12KT 4675 11461 4677 11352