A cold upper level closed low brought widespread heavy snow across southwest Montana, west-central Montana and along the Continental Divide. The late season snow storm brought wet heavy snow to many valleys and caused power outages and tree damage.
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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 cold upper level closed low brought widespread heavy snow across southwest Montana, west-central Montana and along the Continental Divide. The late season snow storm brought wet heavy snow to many valleys and caused power outages and tree damage. In southwest Montana, prolonged periods of heavy snow caused Homestake pass to close for many hours.
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 16, 1:12 PM MST, 12 hours 18 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
212 PM MDT Tue May 16 2017
...SNOW DOWN TO 3000 FEET TONIGHT ACROSS NORTHERN ROCKIES...
.DISCUSSION...A significant and complex storm system is still
expected to swing through the Northern Rockies tonight through
Thursday morning. The first aspect of the system will be a cold
front finishing its push through the Northern Rockies this
afternoon and evening bringing widespread precipitation. Snow
levels will remain relatively high during this frontal passage,
so any snow should be limited to the higher terrain. As the center
of the low pressure system moves into southwest Idaho, the second
feature to develop will be a trough of warm air loft (TROWAL),
which is associated with an area of enhance precipitation. This
trowal feature appears to develop over west central Montana later
this evening. The overall model consensus has the the heaviest
precipitation from the southern end of the Bob Marshalls over
Seeley Lake and into the Mission valley. It will be under this
feature that will give the valleys their best chance of impactful
snow, such as heavy snow breaking tree branches causing localize
power outages. Confidence is only moderate on the placement of
this trowal feature, but it will have one of the biggest impacts
to the valleys of western Montana. The low moves into southeast
Idaho and slows down allowing the third and final feature of wrap
around precipitation that will be enhanced by upslope along the
Continental Divide down into this southwest Montana. This will be
a prolong precipitation event that will cause southwest Montana to
receive the heaviest snowfall of all areas. The Butte/Anaconda
area could receive 6 to 8 inches with Georgetown Lake, MacDonald
and Homestake passes getting at least a foot of new snow.
Rain and high-elevation snow showers across the Northern Rockies
will continue through Thursday. Mountain passes along the
Continental Divide could see another dusting of snow turning to
light slush on the pavement Thursday morning, creating a brief
winter driving hazard. Otherwise, a slow warming trend will be
present across the region through Friday with variable cloudiness.
Saturday through Monday, models suggest that mild surge of cool
air from the Canada Prairie will run along the east of the
Continental Divide, increasing precipitation chances and
decreasing snow levels for a time. Snow chances appear greatest
for mountain passes along the Divide Sunday evening through Monday
morning. Most of the snow that falls at mountain pass elevations
will likely turn to slush on the pavement, however there may be a
few hours around sunrise Monday when the snow will stick and
create slick driving conditions on the passes.
Dry and warm high pressure is expected to return to the Northern
Rockies Tuesday and Wednesday next week.
&&
.AVIATION...Winter storm conditions will spread across the
Northern Rockies air space during the next 24 hours. Rain will be
present at times near all area terminals through 17/0200Z, with
cloud bases slowly lowering as well. KBTM will experience a mix of
rain and snow after 17/0200Z, becoming all snow after 17/0600Z
through Wednesday morning. KMSO will experience a mix of rain and
snow after 17/0900Z and continue through Wednesday morning. KSMN
will experience a snow and rain after 17/0500Z, all snow 17/0900Z
through 17/1500Z, and returning to a mix of snow and rain
thereafter. KGPI is anticipated to remain all rain, with the most
significant impact 17/0500Z through 17/1000Z. All snow and
snow/rain mix periods will be accompanied by substantially lowered
ceilings and visibility. Terrain will be obscured for much of the
Northern Rockies, especially after 17/0200Z.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning from 2 AM Wednesday to 9 AM MDT Thursday
ABOVE 5000 FEET for the Butte/Blackfoot Region.
Winter Storm Warning from 9 PM this evening to 2 PM MDT
Wednesday ABOVE 4000 FEET for the Bitterroot/Sapphire
Mountains.
Winter Weather Advisory from midnight tonight to 10 AM MDT
Wednesday Flathead/Mission Valleys...Missoula/Bitterroot
Valleys.
Winter Weather Advisory from 9 PM this evening to noon MDT
Wednesday Lower Clark Fork Region.
Winter Storm Warning from 2 AM Wednesday to 9 AM MDT Thursday
ABOVE 4000 FEET for the West Glacier Region.
Winter Storm Warning from midnight tonight to 9 AM MDT Thursday
ABOVE 3500 FEET for the Potomac/Seeley Lake Region.
ID...Winter Storm Warning from 9 PM this evening to 9 PM MDT
Wednesday ABOVE 4000 FEET for the Eastern Lemhi County...
Western Lemhi County.
Winter Storm Warning from 8 PM this evening to 1 PM PDT
Wednesday ABOVE 4000 FEET for the Southern Clearwater
Mountains.
Winter Weather Advisory from 8 PM this evening to 11 AM PDT
Wednesday Northern Clearwater Mountains.
Winter Weather Advisory from 8 PM this evening to 1 PM PDT
Wednesday ABOVE 4000 FEET for the Lower Hells Canyon/Salmon
River Region.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
931 PM MDT TUE MAY 16 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0900 PM HEAVY SNOW 11 SSE OROGRANDE 45.55N 115.46W
05/16/2017 M3.0 INCH IDAHO ID PUBLIC
REPORTED AT DIXIE,ID.
&&The national radar mosaic for the moment the first event began.
6 heavy snow. Local standard time, as filed.
Lolo and Saddle Mountain snotel recorded 8 to 10 inches of snow. Many hours of moderate to heavy snow caused slick roads over Lolo and Lost trail passes.
A trained spotter reported 11 inches of snow in the Hills of Butte and at least 8 inches of snow in downtown Butte. The prolonged periods of heavy wet snow caused a few semi trucks to jackknife and resulted in Homestake pass being shut down for several hours. Additionally, Barker Lake snotel reported 22 inches, and Warm Springs reported 11 inches of snow with this system.
A trained spotter reported 4 inches at Twin Creeks and saw 10 to 12 inch diameter trees down at Greenough Hill. Similar reports of damage came from Bonner, where they received 1.5 inches. Additionally, reports were received of 6 inches in Potomac and 3 inches in Greenough.
An NWS employee reported 3 inches of heavy wet snow which caused many tree limbs to break off. Also, a spotter in Evaro Hill reported 5 inches of snow.
An NWS employee reported 4.5 inches of snow up in the Rattlesnake valley and 5 inches just north of Florence. Missoula received 2.7 inches of snow, which caused tree damage power outages lasting several hours. The power outage affected nearly 4,000 people according to Northwestern energy. Additionally, snow rates of 1 inch per hour caused slushy, slick roads in the morning hours.
Pike Creek snotel reported 17 inches of snow in less than 24 hours. Additionally, the Department of Transportation reported thick slushy roads, and a few car slide offs.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2017Every state in 2017This day in weather historyWarnings in Montana, May 2017
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: 687711, 687713, 687715, 687705, 687708, 687704.