Yellowstone Weather in September: What to Expect and What to Pack
Monthly averages are NOAA 1991-2020 climate normals. Check the NPS alerts page for road and trail closures before you go.
By John Love I've been here · Sept 2025Facts checked against NPS.gov · Updated October 6, 2026September in Yellowstone69°F days, 39°F nights at Mammoth Hot Springs (6,195 ft), with about 1.2 inches of precipitation and 0.6 inches of snow. Pleasant days and cool nights, with early snow possible at higher elevations. Crowds thin after Labor Day and elk rut activity peaks.
How elevation changes the weather in Yellowstone
Estimated average high and low for each area in September, highest first. Air cools about 3.5°F for every 1,000 feet you climb, so the same day can feel like two different seasons.
- 8,859 ftDunraven Pass60° / 30°
- 7,782 ftYellowstone Lake63° / 33°
- 6,200 ftMammoth Hot Springs69° / 39°
Estimates based on the long-term average at Mammoth Hot Springs (6,195 ft). Check the live forecast for each area above before you go.
September compared with the months around it
| Month | Avg high | Avg low | Precipitation | Snowfall |
|---|---|---|---|---|
| August | 80°F | 46°F | 1.1 in | 0.0 in |
| September | 69°F | 39°F | 1.2 in | 0.6 in |
| October | 54°F | 29°F | 1.3 in | 4.7 in |
September is 11°F cooler than August by day, and October cools another 15°F.
Weather hazards to plan for
- Sudden snowstorms and whiteouts any month at high elevations, including Dunraven Pass and Sylvan Pass, can close roads with little notice.
- Afternoon lightning storms in July and August on exposed ridges, open valleys and lakeshores.
- Extreme winter cold, with nights well below 0°F at Lake, Old Faithful and West Yellowstone; frostbite and hypothermia risk for oversnow travelers.
- Cold water: Yellowstone Lake stays very cold year-round, and capsized boaters can quickly become hypothermic even in summer.
- Wildfire smoke and haze in mid-to-late summer, plus icy, snow-packed roads in spring and fall shoulder seasons.
What to pack for Yellowstone in September
Picked from Yellowstone's average weather in September.
Nights average 39°F at Mammoth Hot Springs, and higher campgrounds run colder. A bag rated about 10°F below the low keeps you warm.
Shop at Coleman
With nights near 39°F, hot meals and drinks make mornings much easier. Stoves are usually allowed even when campfires are banned.
Shop at Coleman
Long, cold evenings come early in September. A rechargeable lantern lights camp without a fire.
Shop at ColemanWarm jacket on AmazonBase layers on AmazonSome links above are affiliate links. If you buy through them, we may earn a commission at no extra cost to you. How this works
Yellowstone in September: questions
What is the weather like in Yellowstone in September?
At Mammoth Hot Springs (6,195 ft), September averages 69°F by day and 39°F at night, with about 1.2 inches of precipitation. Pleasant days and cool nights, with early snow possible at higher elevations. Crowds thin after Labor Day and elk rut activity peaks.
How cold does Yellowstone get at night in September?
Nights average 39°F at Mammoth Hot Springs. Up at Dunraven Pass (8,859 ft) expect it about 9°F colder, near 30°F.
Does it snow in Yellowstone in September?
Yes. Mammoth Hot Springs averages about 0.6 inches of snow in September, and higher areas get more.
How does September compare with August?
September averages 69°F by day, 11°F cooler than August, and October averages 54°F.
What should I wear in Yellowstone in September?
Plan for layers you can add and remove: a fleece or light puffy for mornings and evenings. Check the forecast for each area you will visit a few days before you go.
More for your Yellowstone trip
- Yellowstone National Park guideFees, hours, maps, where to stay and a first-day plan.
- Best Time to Visit Yellowstone National ParkWhen to visit Yellowstone, month by month: road opening and closing dates, crowds, weather, wildlife timing and what is open in each season.
- How Many Days Do You Need in Yellowstone?How many days to spend in Yellowstone, with 1-, 2-, 3- and 4-day itineraries by area, NPS drive times around the Grand Loop and where to base yourself.
- Best Hikes in Yellowstone National ParkThe best day hikes in Yellowstone, from the Grand Prismatic Overlook to Mount Washburn and Avalanche Peak, with NPS distances, elevation gain and 2026 closures.
- Camping in Yellowstone National Park: Campgrounds, Reservations and TipsAll 11 Yellowstone campgrounds with 2026 dates, fees and RV limits, how six-month reservations work, the 2027 move to Recreation.gov and backcountry permits.