SeasonMapBig Sky weather in September
United States
September in Big Sky: nice, a little rain, with clean air — not the best time to visit.
#9 of 12 months in Big Sky · #1334 of 1383 destinations to visit in September · comfort 23/100 (tier F)
Updated September 2026 · climate normals from ERA5 reanalysis
Traveller notes on Big Sky in September
Notes from nearby Bozeman (51 km away)
Big Sky doesn't have its own notes for September yet — these are about Bozeman, close enough to share the season.
Montana's forum calls September a favorite among regulars for exactly the reason you'd expect — good weather, real crowds already thinned from summer — while warning it can swing hard: one visitor described 75°F hiking weather followed by snow the very next day. Layers are the universal advice, not just a light jacket.
Other months in Big Sky
Big Sky's forum calls February prime powder season — deep base depth, frequent storms, and, outside the Presidents Day weekend crush, thinner crowds than the holidays. Regulars say conditions generally hold up well into March, so it's not a narrow window.
Add your own note from Big Sky's card on the map.
Big Sky climate normals — September
| Daytime high | 19°C / 67°F | 😎 nice |
|---|---|---|
| Nighttime low | 7°C / 45°F | |
| Feels like (high) | 17°C / 63°F | |
| Rainfall | 63 mm / 2.5 in | 🌦 some rain |
| Rainy days | 10 days | |
| Humidity | 60% | 🍃 comfortable |
| Dew point | 4°C / 40°F | |
| Sunshine | 10.3 h/day | |
| Daylight | 12.5 h | |
| Wind | 12 km/h / 8 mph | |
| Snowfall | 9 cm / 3.5 in | |
| Air quality (US AQI) | 39 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Crowds in Big Sky in September
How busy the place itself is — school and mass holidays, the months an editor tagged, and how sought-after the weather makes them. Never part of the comfort score.
BusySummer break in United States(estimated)
Peak crowdsBusyShoulder seasonQuiet
Best months for Big Sky's weather
Ranked by this destination's own climate comfort score across the year — a different thing from how busy it gets (see Crowds above).
Fair weatherBig Sky's weather peaks December–February.
Best weatherFair weatherToughest weather
What's on in Big Sky in September
Recurring seasonal events, natural spectacles, closures and holidays — curated and sourced.
- Opening
Yellowstone roads open
15 Apr – 5 Nov · usuallyTrail seasonClosuresThe interior roads out of West Yellowstone are ploughed open in stages from mid-April and close again to cars in early November, after which it is snowcoach or nothing. Big Sky is an hour from that gate. Source ↗
- Festival
Music in the Mountains
1 Jun – 10 Sep · usuallyMajor festivalFree Thursday-evening concerts in Town Center park from early June to the start of September. Bring a blanket and something warm; the temperature drops the moment the sun goes behind Lone Peak. Source ↗
Nearby, and something's on
Within 300 km of Big Sky — a day trip or a short hop — with something on this month. Never part of the comfort score.
Where is Big Sky?
Big Sky in September — FAQ
- Is September a good time to visit Big Sky?
- September in Big Sky: nice, a little rain, with clean air — not the best time to visit. It ranks #9 of 12 months for Big Sky on SeasonMap's comfort score (23/100).
- What is the weather like in Big Sky in September?
- In September, Big Sky averages a daily high of 19.4°C and a low of 7.2°C, with about 62.9 mm of rain over roughly 9.7 rainy days.
- What is the air quality in Big Sky in September?
- Big Sky has a mean US Air Quality Index of about 39 in September.
- Does it snow in Big Sky in September?
- Big Sky sees roughly 9 cm of snowfall in September.
Other months in Big Sky
Compare Big Sky in September
Warmer or cooler than Big Sky in September
Similar destinations in North America — September
Within 300 km: Bozeman's Golden eagle migration around 15 Sep – 31 Oct, and Yellowstone National Park's Beartooth Highway open around 22 May – 12 Oct.