A deep upper-level trough and embedded low pressure center moved southeastward from the Gulf of Alaska. Ahead of this system, isentropic lift generated widespread precipitation.
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 TFX wrote it up.
A deep upper-level trough and embedded low pressure center moved southeastward from the Gulf of Alaska. Ahead of this system, isentropic lift generated widespread precipitation. This included accumulating snow in the mountains, especially above 6000 feet MSL. Greater snow amounts were realized in the Central and Southwest Montana mountains compared to farther north.
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 Great Falls, MT wrote its last area forecast discussion before the first event at Sep 15, 4:27 AM MST, 2 hours 40 minutes earlier.
Area Forecast Discussion National Weather Service Great Falls MT 527 AM MDT Fri Sep 15 2017 ...Updated Aviation Discussion... .SYNOPSIS... Widespread rain and mountain snow will continue to develop across the area today and continue into Saturday. This is the first significant snowfall of the season for higher elevations, and the first significant rainfall for much of the area since June. An overall cooling trend is expected through the end of the week. && .DISCUSSION... Today through Sunday night... There remains little change with the forecast through the first half of Saturday. Impressive upper-level low just to our west along with equally impressive mid-level isentropic lift are combining to produce widespread rain across north-central and southwest Montana. Rain, and mountain snow, will end from west to east Saturday with the passage of the upper-level trough. The westerly mid-level flow behind this system will help induce a surface lee-side trough late Saturday into Sunday. This should help produce some cross-barrier flow across the Rocky Mountains and the Continental Divide overnight Saturday night into Sunday morning, which should in turn provide just enough wind to keep temperatures from dropping to freezing or below over the adjacent plains. However, this is still somewhat low confidence and will bear watching. Flat, progressive upper-level ridging moves overhead Sunday before another storm begins to approach from the Northeast Pacific late Sunday night. CC Monday through Friday...All models continue in good agreement with a very strong upper level disturbance swinging across the NW US in the beginning of next week. For this region, a fast-moving cold front will eject eastward which will likely cause some rain showers, or perhaps a few thunderstorms for central and southern areas during the afternoon and evening hours on Monday. Simultaneously, a deep lee-side surface low will begin to develop just across the Canadian border to the north. This will lead to increasing pressure gradient winds, coupled by increasing 700mb winds aloft to create breezy conditions beginning on Tuesday. The aforementioned upper level disturbance will then likely close off, allowing for the surface low to stall just to the north which will keep the area in an unsettled pattern through the rest of the week along with continued windy conditions. Expect chances of rain showers, persistent cloud cover and cool temperatures to last well through the end of the week with temperatures ranging 5 to 15 degrees below climatological normal for this time of the year. KLG && .AVIATION... Updated 1127z. Upper level low pressure trough will remain over the Northern Rocky Mountain region through tonight, then eject east across our area Saturday. Widespread low- and mid-level cloud cover will produce a mix of LIFR/IFR/MVFR ceilings with periods of precipitation and fog lowering visibilities as well. Snow levels have dropped to near 5000 feet with clouds and areas of heavy snow producing mountain obscurations. Reduced ceilings and visibility should prevail through the entire forecast period for most of the forecast area. CC && .PRELIMINARY POINT TEMPS/POPS... GTF 44 36 49 35 / 100 100 70 10 CTB 46 34 51 32 / 80 60 50 10 HLN 43 36 50 34 / 100 100 70 10 BZN 44 35 48 31 / 100 100 70 10 WEY 41 31 43 27 / 90 80 60 10 DLN 41 33 48 32 / 100 100 60 10 HVR 51 40 52 36 / 70 70 60 20 LWT 42 35 46 33 / 100 100 80 30 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until noon MDT Saturday above 5500 feet for Broadwater...Cascade...Central and Southern Lewis and Clark... Jefferson...Judith Basin...Meagher...Southern Rocky Mountain Front. Winter Storm Warning until noon MDT Saturday above 6500 feet for Beaverhead...Gallatin...Madison. Winter Weather Advisory until noon MDT Saturday above 6000 feet for Northern Rocky Mountain Front. && weather.gov/greatfalls
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
652 AM MDT FRI SEP 15 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0615 AM SNOW 14 NW WOLF CREEK 47.17N 112.25W
09/15/2017 M1.0 INCH LEWIS AND CLARK MT NWS EMPLOYEE
1 INCH OF SNOW HAS ACCUMULATED AT THE ALICE CREEK FIRE
ICP AND IT IS STILL SNOWING. THE COMBINATION OF RAIN AND
SNOW IS MAKING IT DIFFICULT TO MOVE FIRE EQUIPMENT
AROUND. ELEVATION 4700 FEET.
&&
MARTINPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
734 AM MDT FRI SEP 15 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0732 AM HEAVY RAIN 8 SE ULM 47.35N 111.39W
09/15/2017 M1.51 INCH CASCADE MT TRAINED SPOTTER
EVENT TOTAL RAINFALL THROUGH 730 AM. STILL RAINING.
&&
MARTINPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
747 AM MDT FRI SEP 15 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0745 AM HEAVY RAIN 15 SE CHECKERBOARD 46.42N 110.33W
09/15/2017 M1.00 INCH MEAGHER MT PUBLIC
RAINFALL TOTAL THUS FAR THROUGH THE EVENT ALSO 24HR
TOTAL FOR THURSDAY... SEPTEMBER 14TH
&&
MOLDAN5 winter storm. Local standard time, as filed.
MT DOT webcam showed snow-covered roadway along MacDonald Pass. Also snowing steadily at the time. Elevation: 6320 feet MSL.
MT DOT webcam showed snow-covered roadway along I-15 at Boulder Hill. Visibility was also reduced greatly by falling snow. Elevation: 5600 feet MSL.
Glacier Park reported Logan Pass was closed temporarily due to winter storm conditions.
Trained spotter reported up to 4 inches of snow in Dillon. Also received multiple reports of vehicle slide-offs along I-15 on his scanner.
Google Traffic showed very slow traffic flow over Rogers Pass. Likely due to falling snow per radar imagery.
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, September 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: 714655, 718921, 714660, 714658, 714668.