A colder than normal mid and upper level low moved from western Washington early on September 25th to southern Idaho before it split into two separate systems. One moved to the north and east into eastern Montana while the other sagged south into Utah by the 26th.
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 colder than normal mid and upper level low moved from western Washington early on September 25th to southern Idaho before it split into two separate systems. One moved to the north and east into eastern Montana while the other sagged south into Utah by the 26th. On the northern periphery of this system in elevations above 5,000 feet, up to 18 inches of snow fell creating travel impacts, power outages and vegetation 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 Sep 25, 5:45 AM MST, 6 hours 15 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
645 AM MDT Wed Sep 25 2013
.DISCUSSION...
Scattered showers will continue to spread
northeastward out of central Idaho this morning. Valleys of west-
central and northwestern Montana will see another cool and wet day
today.
As the low pressure moves south and east, cold air will move in
and lower snow levels to around 5000FT. Glacier National Park and
surrounding mountains will continue to see off and on snow
showers impacting the Going To The Sun Road and other local
mountain roadways, therefore the winter storm warning will
continue. By mid day into the later afternoon, rain will
transition over to snow across southwestern Montana and Lemhi
county of Idaho. Mountain passes in these regions are still on
track to receive up to a foot of snow through the day and overnight.
High elevation valleys including Butte, Anaconda, and Georgetown
Lake will see up to 6 inches, localized areas could see slightly
higher amounts. The impacts in these areas could be great. Heavy wet
snow has the potential to bring down trees and limbs, as well as
power lines. Road conditions will also be an impact due to snow
cover. Winter storm warnings in these regions will remain until
noon tomorrow.
Another impact will be after the storm moves off to the east. Cold
air is expected to remain in place, creating a cold start to the
day Friday morning. Many locations in western Montana and central
Idaho will see temperatures below freezing. Sensitive plants
left unattended are at risk due to the freezing temperatures.
Uncertainty still dominates the weekend forecast. Over the last 24
hours, models have flipped to a wetter solution for Sunday through
early next week. The reason is the extreme sensitivity of the
forecast to the details of the transition of tropical cyclone
Pabuk to a winter storm off the Japanese east coast. The effects
of that transition will ripple down stream and impact the weather
over the northern Rockies this weekend.
Central Idaho and northwestern Montana are most at risk for a few
days of rain and high elevation snow Sunday and Monday.
Southwestern Montana and Lemhi County, Idaho may have some
precipitation, but it will be a low impact event. Raised
probability of precipitation and lowered temperatures Sunday
through next week toward the shifting model consensus. Expect much
better confidence in next week's forecast over the next few days
as Pabuk finishes its transition.
&&
.AVIATION...All aviation sites will be impacted in some way today.
KMSO, KGPI, and KSMN will see low ceilings with rain showers for
much of the day. KMSO and KGPI will also see the potential for
reduced visibility this morning. KBTM will start the day off with
rain showers then transition over to snow later this afternoon. Snow
is expected to continue into the overnight hours into tomorrow
afternoon. Mountain obscurations will exist throughout western
Montana and central Idaho all day today.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WARNING from 6 PM this evening to Noon MDT Thursday
ABOVE 5000 FEET FOR THE Butte/Blackfoot Region.
WINTER STORM WARNING from Noon today to Noon MDT Thursday ABOVE
6000 FEET FOR THE Bitterroot/Sapphire Mountains.
WINTER STORM WARNING until Midnight MDT tonight ABOVE 6000 FEET
FOR THE West Glacier Region.
ID...WINTER STORM WARNING until Noon MDT Thursday ABOVE 6000 FEET FOR
THE Eastern Lemhi County.
&&
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https://www.twitter.com/NWSMissoulaThe national radar mosaic for the moment the first event began.
3 heavy snow, 2 winter weather. Local standard time, as filed.
A person from the public in Leadore (5,900 ft.) estimated that 2 inches of snow fell during the storm.
A person from the public 5 miles south-southeast of Leadore estimated that 6 inches of snow fell.
Webcams from Lost Trail Pass (7,090 ft.) revealed snow-covered roads for much of the evening on the 25th through the morning hours of the 26th. The nearby Saddle Mountain SNOTEL located at 7,900 ft. measured 6 inches of snow with 0.90 of snow water equivalent. The pass had to be plowed often during the night which is a rare occurrence and quite possibly due to the unseasonable nature of this event.
The Idaho Transportation Department estimated 5 inches of snow that fell at Gilmore Summit at 7,186 ft. Webcams revealed snow-covered roads at times during the event.
The Morgan Creek SNOTEL located 30 miles southwest of Salmon at 7,600 ft. measured 5 inches of snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2013Every state in 2013This day in weather historyWarnings in Idaho, September 2013
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: 474326, 474325, 474321, 474324, 474323.