Great Falls, MT weather in September
Expect mild weather with some rain in Great Falls in September, with highs near 72°F and lows near 43°F. Rain or snow falls on about 7 days. Snowfall averages about 0.8 in. Good for outdoor plans.
- Normal high
- 72°F
- Normal low
- 43°F
- Wet days
- 7
- 1.3 in total
- Snowfall
- 0.8 in
- normal snowfall
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 78°F | 65°F |
| Normal low | 47°F | 39°F |
| Chance of a wet day | 23% | 24% |
| Sunrise / sunset | 6:44 am / 8:06 pm | 7:23 am / 7:07 pm |
| Daylight | 13.4 h | 11.7 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Mountain Time).
A typical September day
- 6 am47°Fdew point 37°F
- 9 am57°Fdew point 38°F
- Noon66°Fdew point 37°F
- 3 pm69°Fdew point 36°F
- 6 pm64°Fdew point 37°F
- 9 pm55°Fdew point 37°F
NOAA hourly normals (local standard time) from Great Falls Intl Airport (4 mi away); average wind 10 mph; clear or few clouds in 71% of daytime hours, mostly cloudy or overcast in 23%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F14 of 30
- Hot dayshigh 90°F or more2 of 30
- Muggy daysdaily mean dew point 65°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow7 of 30
- Notable rainat least 0.10 in3 of 30
- Freezing nightslow 32°F or below2 of 30
- Snow on the groundsnow depth 1 in or more0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain and snow in September
Normal precipitation is 1.3 in; a dry September brings about 0.9 in and a wet one about 1.8 in (25th and 75th percentiles). About 1 day brings half an inch or more. Normal snowfall is 0.8 in.
How September varies from year to year
- Warmest September, 1991-20202009: average high 80°F
- Coolest September1993: average high 65°F
- Wettest September2015: 2.5 in
- Driest September2012: no measurable precipitation
- Highest reading97°F (September 5, 2020)
- Lowest reading12°F (September 30, 2019)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 83°F | 72°F | 57°F |
| Normal low | 50°F | 43°F | 33°F |
| Wet days | 7 | 7 | 7 |
| Comfortable days | 9 | 14 | 8 |
| Daylight | 14.2 h | 12.6 h | 10.8 h |
Highs change by -11°F from August and -15°F into October.
How Great Falls ranks in September
- Normal high331st warmest of 378 cities; 3rd of 6 in Montana
- Wet days154th driest of 378
- Comfortable days94th most of 342
What to pack for Great Falls in September
- Layers – afternoons near 72°F but nights near 43°F
Frost in September
The first fall frost typically comes around Sep 24; in 1 year in 10 it comes before Sep 9. All frost dates for Great Falls.
Heating and cooling
September has 258 heating degree days and 25 cooling degree days (base 65°F), 4% of the year's total heating and cooling demand.
Questions
How hot is Great Falls in September?
The normal high is 72°F and the normal low is 43°F. From 1991 to 2020 the hottest September reading was 97°F (September 5, 2020).
Does it rain a lot in Great Falls in September?
About 7 days in September have at least 0.01 in of precipitation, and the normal total is 1.3 in. The wettest September in 1991-2020 was in 2015 (2.5 in); the driest was in 2012, with no measurable precipitation.
Does it snow in Great Falls in September?
Yes. Normal snowfall in September is 0.8 in.
Is September a good time to visit Great Falls?
September ranks 3rd of 12 months on our comfort score for Great Falls (69 out of 100). It has about 14 comfortable days and about 2 days at 90°F or hotter. The best month is June.
Where the numbers come from
- Temperature, rain, snowfall, snow depth, frost dates, humidity and wind by hour and cloud cover: Great Falls Intl Airport (USW00024143), 4.2 mi WSW of the city center, 3,664 ft (335 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Great Falls International Airport (727750-24143), 4.3 mi WSW of the city center, 3,667 ft (338 ft higher than the city). Hourly observations, 1991-2020.