Big Sky, MT weather in September
Expect mild weather with some rain in Big Sky in September, with highs near 68°F and lows near 33°F. Rain falls on about 10 days. Great for outdoor plans.
- Normal high
- 68°F
- Normal low
- 33°F
- Wet days
- 10
- 1.7 in total
- Daylight
- 12.5 h
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 73°F | 62°F |
| Normal low | 36°F | 30°F |
| Chance of a wet day | 34% | 31% |
| Sunrise / sunset | 6:47 am / 8:03 pm | 7:22 am / 7:08 pm |
| Daylight | 13.3 h | 11.8 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Mountain Time).
What kind of days to expect
- Comfortable dayshigh 65-80°F (temperature only: no humidity station nearby)20 of 30
- Hot dayshigh 90°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow10 of 30
- Notable rainat least 0.10 in5 of 30
- Freezing nightslow 32°F or below15 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain in September
Normal precipitation is 1.7 in; a dry September brings about 0.8 in and a wet one about 2.2 in (25th and 75th percentiles). About 1 day brings half an inch or more.
How September varies from year to year
- Warmest September, 1991-20202009: average high 75°F
- Coolest September2004: average high 66°F
- Wettest September1997: 3.5 in
- Driest September1993: no measurable precipitation
- Highest reading89°F (September 8, 2020)
- Lowest reading12°F (September 24, 2000)
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 | 77°F | 68°F | 53°F |
| Normal low | 39°F | 33°F | 25°F |
| Wet days | 11 | 10 | 10 |
| Comfortable days | 18 | 20 | 6 |
| Daylight | 14.1 h | 12.5 h | 10.9 h |
Highs change by -9°F from August and -15°F into October.
Nearby alternatives in September
- Warmer: Billings, MT143 mi · high 75°F · 7 wet days
- Drier: Sun Valley, ID183 mi · high 69°F · 4 wet days
How Big Sky ranks in September
- Normal high358th warmest of 378 cities; 5th of 6 in Montana
- Wet days292nd driest of 378
What to pack for Big Sky in September
- A warm jacket – lows near 33°F, highs near 68°F
- Layers – afternoons near 68°F but nights near 33°F
- A rain jacket or umbrella – rain on about 10 days
- A hat and gloves – about 15 freezing nights
Heating and cooling
September has 428 heating degree days and 0 cooling degree days (base 65°F), 4% of the year's total heating and cooling demand.
Questions
How cold is Big Sky in September?
The normal high is 68°F and the normal low is 33°F. From 1991 to 2020 the coldest September reading was 12°F (September 24, 2000).
Does it rain a lot in Big Sky in September?
About 10 days in September have at least 0.01 in of precipitation, and the normal total is 1.7 in. The wettest September in 1991-2020 was in 1997 (3.5 in); the driest was in 1993, with no measurable precipitation.
Is September a good time to visit Big Sky?
September ranks 4th of 12 months on our comfort score for Big Sky (76 out of 100). It has about 20 comfortable days (judged by temperature only). The best months are June, July and September.
Where the numbers come from
- Temperature and rain: Big Sky 2WNW (USC00240775), 2.1 mi ESE of the city center, 6,590 ft (630 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Not available for this location: snowfall, snow depth, frost dates, humidity and wind by hour, cloud cover and daily humidity and wind (no station close enough or similar enough in elevation).