Widespread snow impacted higher elevations of western Montana and north central Idaho, including mountain pass areas.
Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS MSO wrote it up.
Widespread snow impacted higher elevations of western Montana and north central Idaho, including mountain pass areas.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Missoula, MT wrote its last area forecast discussion before the first event at Dec 11, 1:39 PM PST, 21 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
239 PM MST Tue Dec 11 2018
.DISCUSSION...Winter weather advisories and warnings are in
effect for multiple and various impacts across the Northern
Rockies. A strong winter storm is beginning to impact the region
with mountain snow over Lookout Pass. Snow will begin to pick up
in intensity and coverage across all of the region's mountain
passes late this afternoon and evening. However MacDonald and
Homestake passes will escape with minimal snowfall and impacts.
Expect moderate to heavy snow at times with some occasional
snowfall rates of 1 inch per hour. Lower valleys in central Idaho
will see a mix of rain snow and freezing rain this evening.
For locations in and around Grangeville, Idaho. We are expecting
light snow accumulations, though the biggest threat will be strong
gusty southerly winds that have the potential to gust up to 55
mph. The southerly cross winds along Highway 95 from Grangeville
west to Cottonwood, could become hazardous to high profile
vehicles, and visibility due to blowing snow. Current forecast
have the strongest winds from sunset this evening to sunrise
tomorrow morning.
Snowfall is expected in the valleys of western Montana later
tonight through the Wednesday morning commute. Snowfall amounts
aren't expected to be more than 1-3" however some strong snow
bands are expected to materialize late tonight and Monday morning
and bring locally moderate to heavy snow. Strong winds in and
around the snow bands could produce blowing snow impacting
visibilities for travelers. Some areas of concern for travelers
will be the S curves between Missoula and Lolo as well as the I-90
corridor from Clinton to Butte. Sporadic power outages are
possible due to winds gusting up to 40 mph, with isolated higher
winds in the Bitterroot valley. The stronger winds are expected
to arrive around midnight tonight, and continue until mid morning
tomorrow.
The winds will gradually diminish from west to east during the day
on Wednesday. Gusty winds up to 40 to 45 mph will continue along
I-90 from Dearlodge to Butte through most of the day.
The remainder of this week into next week will bring periods of
unsettled weather, aka wind and mountain snow, as several weather
disturbances are expected to move in and around the vicinity of
the Northern Rockies. Temperatures will be at or above normal
through next week. In fact, the Missoula and Bitterroot valleys
can expect high temperatures in the mid and possibly upper 40s
Friday. Overnight lows will be in the lower to mid 20s through
next week. No major cold outbreaks are expected through the middle
of next week.
&&
.AVIATION...High clouds have moved in from the west and winds are
increasing from the south and southwest. Overnight a Pacific
weather system will affect the entire forecast area. Bringing
light snow to the valleys and heavy snow to mountain passes of the
Idaho and Montana line. Winds in the Bitterroot and Missoula
Valleys will increase to 15 to 25 gusting to 40 Kts affecting MSO
and BTM. Wednesday early morning through afternoon expect low
ceilings and obscured terrain due to moderate snow. Also
visibility will be affected by blowing snow and periods of
moderate snow. Conditions will slowly improve through the
afternoon.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 8 PM this evening to 11 AM MST
Wednesday Butte/Blackfoot Region.
Winter Storm Warning until 11 AM MST Wednesday
Bitterroot/Sapphire Mountains.
Winter Weather Advisory from 8 PM this evening to 11 AM MST
Wednesday Missoula/Bitterroot Valleys.
Winter Storm Warning until 11 AM MST Wednesday Lower Clark Fork
Region.
Winter Weather Advisory from 8 PM this evening to 11 AM MST
Wednesday Flathead/Mission Valleys.
Winter Storm Warning until 11 AM MST Wednesday West Glacier
Region.
Winter Weather Advisory until 9 AM MST Wednesday
Kootenai/Cabinet Region.
Winter Weather Advisory from 5 PM this afternoon to 11 AM MST
Wednesday Potomac/Seeley Lake Region.
ID...Winter Weather Advisory from 8 PM this evening to 11 AM MST
Wednesday Eastern Lemhi County...Western Lemhi County.
Winter Weather Advisory until 4 AM PST Wednesday
Orofino/Grangeville Region.
Winter Storm Warning until 10 AM PST Wednesday Northern
Clearwater Mountains...Southern Clearwater Mountains.
&&The national radar mosaic for the moment the first event began.
2 winter storm. Local standard time, as filed.
A period of heavy snowfall led to 12 inches of snow in Pierce and generally 7 to 14 inches elsewhere. Areas of blowing snow were also an issue on Highway 11 near Greer Grade.
A period of heavy snowfall created impacts to travel over Lolo Pass on Highway 12, with up to 14 inches of snowfall being reported.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2018Every state in 2018This day in weather historyWarnings in Idaho, December 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 796916, 796919.