A cold upper level closed low brought widespread heavy mountain snow to central Idaho and Lemhi county. The late season snow storm brought wet heavy snow to a few valleys such as Pierce 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 mountain snow to central Idaho and Lemhi county. The late season snow storm brought wet heavy snow to a few valleys such as Pierce and caused power outages and tree damage.
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 17, 1:42 AM PST, 1 hour 18 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
342 AM MDT Wed May 17 2017
...Significant mountain snow today across the Northern Rockies...
.DISCUSSION...At the time of writing this (3AM MDT), rain has
started to turn to snow for elevations as low as 3200 feet across
west-central Montana. Snow has started to accumulate on area
roads above 5000 feet this morning across west-central and
southwestern Montana, and for areas in north-central Idaho. Aside
from slick roads due to snow, one of the main impacts will be for
those who see the snow accumulating on leafed out trees. The
weight of snow could lead to falling tree branches, scattered
power outages, and even some trees falling over where
accumulations are greatest. The likelihood of this occurring is
highest in locations that currently have Winter Storm
Warnings...see www.weather.gov/missoula. One area that will need
to be watched for possible upgrades from advisories to warnings
early this morning, will be the southern Mission Valley and the
Missoula/Bitterroot Valleys. The enhanced area of precipitation
(what we call a TROWAL) has set up over these locations. If
moderate to heavy snow begins to fall in these areas, and looks
continue for a couple hours, warnings may need to be issued.
The TROWAL feature is forecast to drift south into southwestern
Montana later this morning and afternoon, continuing the snowfall
in these locations above 5000 feet. Slight warming in the lower
elevations will allow for the snow to transition back to rain. The
wet and snowy spring storm will linger over the region throughout
the day, into the overnight hours (mainly for southwestern MT and
the Continental Divide). Several inches of snow is still forecast
to occur in locations that are under the warnings.
By Thursday, the system that brought widespread rain and snow
will have moved to the southeast of the area. Southwest Montana
and Lemhi County Idaho could continue to see showers as Gulf of
Mexico moisture continues to be wrapped around the north side of
the low pressure. Temperatures remain cool during the day, and
remain well below seasonal averages, but will be 10 or so degrees
warmer than Wednesday's temperatures. The Northern Rockies look
to be free of any influence of the low by Thursday night.
On Friday the large scale pattern changes to northwest flow.
Isolated afternoon showers are possible, but these will be mainly
confined to the terrain. Temperatures warm another 5 to 10
degrees. A shortwave trough coming in from the northwest will be
the next system to impact the area Saturday night into Sunday, but
temperatures will be warmer by this time, so scattered rain
showers should be the extent of the impact with this system. Those
along the Continental Divide will see these enhanced showers
Sunday into Monday as the trough over the central U.S. brings in
moisture from Canada. Those west of the Divide will be drier, with
partly cloudy skies.
After several consecutive days of warming by a few degrees,
temperatures are forecast to be slightly above average for the
first part of next week, with upper 60s into the 70s for most.
Models disagree mid-week onward, so forecast confidence is low
past this point.
&&
.AVIATION...The spring snowstorm is in full force this morning
across the Northern Rockies. Mountain snow and valley rain will
continue for much of the day for all area terminals. KBTM and KSMN
will primarily see snow this morning and afternoon. A few inches
of snow will be possible by this afternoon for these two terminals.
Currently a rain/snow mix is falling at KMSO, and may change to
all snow for a period of time between 17/1000Z - 17/1500Z, which
will further reduce visibility and lower ceilings. If KMSO does
see the change to all snow, a brief accumulation of 1 to 2 inches
of snow is possible. Terrain obstructions can be expected
throughout the Northern Rockies into the overnight hours tonight.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning until 9 AM MDT Thursday ABOVE 5000 FEET for
the Butte/Blackfoot Region.
Winter Storm Warning until 2 PM MDT this afternoon ABOVE 4000
FEET for the Bitterroot/Sapphire Mountains.
Winter Weather Advisory until 10 AM MDT this morning
Flathead/Mission Valleys...Missoula/Bitterroot Valleys.
Winter Weather Advisory until noon MDT today Lower Clark Fork
Region.
Winter Storm Warning until 9 AM MDT Thursday ABOVE 4000 FEET for
the West Glacier Region.
Winter Storm Warning until 9 AM MDT Thursday ABOVE 3500 FEET for
the Potomac/Seeley Lake Region.
ID...Winter Storm Warning until 9 PM MDT this evening ABOVE 4000 FEET
for the Eastern Lemhi County...Western Lemhi County.
Winter Storm Warning until 1 PM PDT this afternoon ABOVE 4000
FEET for the Southern Clearwater Mountains.
Winter Weather Advisory until 11 AM PDT this morning Northern
Clearwater Mountains.
Winter Weather Advisory until 1 PM PDT this afternoon ABOVE 4000
FEET for the Lower Hells Canyon/Salmon River Region.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
440 AM MDT WED MAY 17 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0430 AM SNOW 3 E FLORENCE 46.63N 114.01W
05/17/2017 M0.5 INCH RAVALLI MT NWS EMPLOYEE
HALF AN INCH OF SNOW ON GRASSY SURFACES. NO
ACCUMULATIONS ON ROADS AS OF 4:30AM.
&&
LVThe national radar mosaic for the moment the first event began.
2 heavy snow. Local standard time, as filed.
Lolo snotel reported 10 inches of snow and Mountain Meadows snotel reported 11 inches of snow. Additionally, a COOP in Dixie reported 5.4 inches of heavy wet snow.
A COOP observer in Pierce reported 4.2 inches of snow which caused power outages and knocked down many cottonwood trees. Shanghai summit snotel just north of Pierce 11 inches of snow with 1.8 inches of Snow Water Equivalent.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2017Every state in 2017This day in weather historyWarnings in Idaho, 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: 687718, 687719.