A moist and unstable air mass settled in over western Montana ahead of an upper level low for Memorial Day weekend. This caused snow levels to lower to the higher urban areas and high-use recreation areas in western Montana.
Every event with a place to put it; 5 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.
A moist and unstable air mass settled in over western Montana ahead of an upper level low for Memorial Day weekend. This caused snow levels to lower to the higher urban areas and high-use recreation areas in western Montana.
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 May 24, 1:56 PM MST, 4 hours 4 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
256 PM MDT Thu May 24 2012
.DISCUSSION...A weak shortwave will help keep scattered showers
around for western Montana and central Idaho into the night time
hours. The showers will mainly stay anchored to the mountains with
the occasional shower drifting into valley locations.
Friday a strong surface gradient will develop along the
Continental Divide ahead of a low pressure developing to the
southwest. This will usher in very strong east winds all along the
divide into western Montana. Valley locations will see sustained
east winds 20 to 30 mph with gusts reaching up to 40 mph. East-west
facing canyons like Bad Rock canyon and Hellgate canyon could see
gusts approaching 50 mph. High winds will create very choppy
conditions on Flathead Lake approaching 5 feet or more...this will
be hazardous to smaller boat craft. A wind advisory has been
issued generally for locations along and north of Interstate 90 in
western Montana. The winds will begin to diminish Saturday morning
as the low pressure system moves closer from the southwest. The
system will begin to affect southwestern Montana and central Idaho
with mountain snow and valley rain by Saturday morning. Snow
levels will be confined to 5500 feet for Lemhi county and the
Bitterroot/Sapphire mountains. Four to 6 inches of snow are expected
for the higher elevations and 1 to 3 inches for Georgetown Lake
and Butte areas. Due to the spring snow accumulations...a winter
weather advisory has been issued for these areas starting at 6am
Saturday morning till 6am Sunday.
The low pressure system will slowly move to the northeast and wrap
more moisture into regions around Glacier National Park by
Saturday afternoon. Twelve to 16 inches of snow are expected to
accumulate in the higher terrain of the park around Logan Pass and
4 to 6 inches of snow in the lower elevations above West Glacier.
Due to the heavy snow amounts and blowing snow...A winter storm
warning has been issued starting at noon on Saturday to midnight on
Sunday. Those planning outdoor activities for this holiday weekend
should be prepared for the combination of wet, cold and windy
conditions, especially if recreating in the higher terrain.
The northern Rockies may get a dry period beginning mid next
week, however timing and confidence is low at this time due to
model discrepancies.
&&
.AVIATION...Widespread showers will continue across western
Montana and north central Idaho this afternoon and evening,
decreasing after sunset. A few of these showers may occasionally
produce a few lightning strikes. Mid and high level cloud cover
associated with these showers will cause much of the higher
terrain to be obscured. A strong easterly gradient will develop
this evening, first across northwest Montana around 25/0300z and
then into southwest Montana by 25/1200z. Winds will become quite
gusty area wide by 25/1800z. Gusts between 35 to 40 knots are
possible Friday afternoon.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY from 6 AM Saturday to 6 AM MDT Sunday
Butte/Blackfoot Region...Potomac/Seeley Lake Region.
WIND ADVISORY from 11 AM to 9 PM MDT Friday Butte/Blackfoot
Region...Potomac/Seeley Lake Region.
WINTER WEATHER ADVISORY from 6 AM Saturday to Midnight MDT
Saturday Night ABOVE 5500 FEET FOR THE Bitterroot/Sapphire
Mountains.
WIND ADVISORY from 11 AM to 9 PM MDT Friday Kootenai/Cabinet
Region...Lower Clark Fork Region.
WIND ADVISORY from 11 AM to 9 PM MDT Friday Flathead/Mission
Valleys...West Glacier Region.
WINTER STORM WARNING from Noon Saturday to Midnight MDT Sunday
Night For Glacier National Park west of the Continental
Divide.
WIND ADVISORY from 11 AM to 9 PM MDT Friday Missoula/Bitterroot
Valleys.
ID...WINTER WEATHER ADVISORY from 6 AM Saturday to Midnight MDT
Saturday Night ABOVE 5500 FEET FOR THE Eastern Lemhi
County...Western Lemhi County.
&&The national radar mosaic for the moment the first event began.
5 heavy snow. Local standard time, as filed.
The 24 hour snowfall total in Anaconda at 5285 feet was measured at 2 inches.
Overnight snowfall was measured at 3.3 inches, 8 miles south of Butte.
Wet, heavy snow fell 7 miles south of Butte. A spotter reported medium sized tree branches broken by the heavy snow.
Snowfall in Georgetown was measured at 3.5 inches.
Snowfall on the Going to the Sun Highway in Glacier National Park was measured at 12 inches near the pass.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2012Every state in 2012This day in weather historyWarnings in Montana, May 2012
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: 381019, 381015, 381021, 381022, 381023.