Every month in Jackson Hole has its own unique charm for visitors and for outdoor adventure. However, many (including myself) will argue that September is the finest time of year to explore the Tetons and Yellowstone – and for good reason.
The summer crowds begin to taper off in September and the fall foliage starts to pop. In addition, periods of stable weather are common, making it a wonderful time to get outdoors and explore.
In this article, I will first go over many of the weather and conditions factors to consider when planning a visit to Jackson Hole and/or Yellowstone in September. Then, I will go over some of the average temperatures and weather information for the area in September.
Sunny bluebird days are common
While Northwest Wyoming typically sees 1-2 cool and wet storm systems during September, overall it is one of the drier months in the region. Brilliant blue sky days can be expected more often than not.
Historical weather records show that Jackson Hole and Yellowstone experience fewer days of measurable precipitation in September than in any other month of the year!
The weather station in Jackson averages only 6 days of measurable precipitation in September. The weather station at Old Faithful in Yellowstone averages 8 days of measurable precipitation.
Even if you only spend a few days in the area, the odds are favorable that you will experience at least one clear day as cloudy/rainy periods tend to last only 1-2 days at a time.
Thunderstorms are less frequent
Thunderstorms are common across the Tetons and Yellowstone in June, July, and August. However, the frequency of storms decreases during the month of September.
The reason is that we start to lose two of the key ingredients for thunderstorms by late summer and early fall: moisture and heating.
By late summer, the atmosphere tends to dry out as near-surface moisture decreases after a summer full of warmth and evaporation, and intrusions of subtropical (or monsoonal) moisture from the south also become less common.
In addition, the days are getting much shorter by early September and the nights are getting colder. Both of these factors limit the amount of atmospheric instability that occurs due to prolonged heating from the sun compared to the longer and hotter days of midsummer.
Thunderstorms still occasionally happen in September. During the early part of the month, subtropical moisture from the south may reach Wyoming on occasion and lead to a day or two of isolated thunderstorms.
By mid to late September, any thunderstorms that are occur will most likely be frontal-driven. Typically, a cold front associated with a Pacific storm system will approach and trigger a round of thunderstorms at the leading edge. Then colder temperatures and widespread non-thunderstorm precipitation arrives behind the front.
So while the Jackson Hole region usually experiences a few thunderstorm days each September, they are much less common compared to prior months.
Jackson Hole and Yellowstone are not exactly known for having hot temperatures compared to most places. That being said, the high altitude sun is quite strong in the summer time. When temperatures are in the 80s and you factor in the sun, it can still get rather toasty while hiking or mountain biking.
In September, temperatures are just about perfect. Yes, nights and mornings can be quite chilly. But the combination of cool mornings and warm afternoons lead to ideal hiking conditions in my opinion.
If you’re camping, the nights will be noticeably colder in September compared to the summer. Don’t let that stop you from camping – just be sure to pack appropriately, and expect temperatures to fall below freezing at night.
In the Jackson Hole valley at about 6,400ft of elevation – average highs range from the mid 70s in early September to mid 60s in late September. Average lows range from mid 30s in early September to upper 20s in late September.
A good rule of thumb at this time of year to estimate higher elevation daytime temperatures on clear days is to subtract 5 degrees F for every 1,000ft of elevation gain.
For nighttime temperatures or cloudy/rainy days this rule of thumb doesn’t apply. Valley inversions are common at night and during early mornings during clear weather. When this happens, the coldest temperatures settle in the valleys, while warmer temperatures hold higher up in the mountains.
Good time to climb peaks in the Tetons
The first significant high elevation snowfall usually arrives at some point in September. However, before this occurs (or even after, if there is melting) can be a great time to bag some of the higher peaks in the Tetons.
Lingering snowpack from the previous winter is at its lowest point in September. And as mentioned earlier, thunderstorms are less common and stable blue sky days are more common.
If you plan on climbing one of the Teton peaks, the first two weeks of September are your best bet. Late September can still be good in some years, it just varies. I will explain the snow potential in September below…
First high elevation snows usually arrive in September
Typically the first significant snowfall of the season at the higher elevations occurs at some point in September. The timing of this does vary significantly from year to year. Since living in Jackson, I’ve seen the first meaningful snows at the 9,000-10,000ft level occur as early as late August, and as late as early October.
In some years it may snow heavily on the peaks in early September (or late August), but then it may dry out for 3 weeks with good climbing conditions in late September. This is what happened in 2018. The high elevations got a heavy snowfall in late August, but it melted and then it didn’t snow up high for all of September.
On the flip side, September 2017 was unseasonably warm (and dry) through mid-month with many days in the 80s in the valley. Then after the 15th, the pattern abruptly shifted into an extended period of unseasonably cold and wet weather. This pattern persisted through the end of the month and left the high elevations covered in snow for the rest of the year, and thus put an early end to climbing season on the peaks.
Most years, there will be 1-2 meaningful snowfalls at the high elevations in September with good melting following the snow events (except on high elevation shaded north faces). However, you just never know year to year. So be sure to keep up with the weather pattern ahead of your trip.
At the lower elevations – snow occasionally falls in the Jackson Hole Valley in late September, and more commonly across Yellowstone. However, accumulating snow in Jackson is rare in September. While light accumulations can and do occur in Yellowstone and the Northern Jackson Hole Valley, it melts quickly afterwards.
If you’re lucky, in late September you might get to see the combination of snow and fall colors. This doesn’t happen every year, but it’s pretty cool when it does occur.
Outstanding Fall Colors
September is fall foliage season in Jackson Hole. The aspen tree turn to gold and put on a spectacular display in the second half of September. It truly is one of the most beautiful times of year.
The peak of fall foliage in Jackson Hole varies year to year, but typically the best bet for peak color is during the last week of September.
However, you can still expect excellent fall colors from mid September through early October every year. Even in early September, the fireweed and grassy shrubs turn a brilliant red and yellow, and the aspens will start to show their first hints of color.
Fall colors are generally better in Jackson Hole and Grand Teton National Park than in Yellowstone. Coniferous trees tend to dominate Yellowstone due to its higher elevation, and deciduous aspen and cottonwood trees are less common.
That being said, there is still good color to be found in Yellowstone in September. It just may be more of the shrubs and grasses variety along with occasional aspen tree.
Bugs are pretty much gone
Mosquitoes and black flies can be annoying across parts of the region in early and mid summer. By September, they are no longer an issue.
Drier conditions and colder nights have taken care of the bugs by this point of the year. Leave the deet at home!
Crowds on the decrease
To be clear, you aren’t going to find an empty Grand Teton or Yellowstone National Park in September. Many people know this is a nice time of year to visit the parks, and the fall foliage is an attraction in of itself.
However, compared to the summer months, the crowds definitely start to dwindle in September. Once the kids are back in school and the concept of a “summer vacation” has passed, you can expect much less tourism traffic after Labor Day.
Better wildlife viewing opportunities
As the temperatures cool and the days become shorter, wildlife becomes much more active starting in September.
The elk rut gets going at this time of year, and you’ll likely hear the bull elk bugling early and late in the day if you’re out hiking in the valleys.
If you’re lucky, you might get to witness the elk rut as the bulls fight for dominance over the cows. It’s a pretty amazing thing to witness, especially when two bull elk charge each other and but antlers.
If you’re hiking in the backcountry, keep in mind that black and grizzly bears become more active as they try to fatten up before winter. Most encounters are harmless, but it’s always a good idea to hike with bear spray.
Moose also become more active in the fall as their mating season begins. They tend to be more unpredictable and occasionally aggressive at this time of year, so be on alert while out on the trails.
Days are getting shorter
One disadvantage of hiking and exploring in September versus the summer months is the shorter days.
On the summer solstice, the sunrise in Jackson is at 5:42am and sunset is at 9:07pm. These are long days! And of course, the light lingers well past sunset in midsummer.
By September, the days are quickly getting shorter. On the 1st (2019), sunrise occurs at 6:46am and sunset at 7:58pm. On the 30th, sunrise occurs at 7:19am and sunset at 7:06pm.
If you have long days planned in the mountains in September, you’ll have noticeably less daylight to work with compared to July. And of course, it’s even more prudent to pack a headlamp and spare batteries in your pack as the days get shorter.
Some campsites and facilities start to close for the season
All roads in Grand Teton and Yellowstone National Parks remain open in September. Developed campsites will stay open through most of September as well, but many will shut down for the season toward the end of the month.
For the exact details on campground open/close dates in Grand Teton and Yellowstone, consult the national park service pages.
Some of the facilities in the parks, such as visitor centers, food establishments, and lodging establishments begin to either close or limit their hours in September as well. Typically this occurs late in the month.
These are probably not issues for those focused on outdoor recreation. But you should still consult the NPS websites just in case you’re planning on a campsite or general store being open.
Average September Temperatures
|Location||Average High||Average Low||Record High||Record Low|
Average September Temperatures by Date
|September 1||September 15||September 30|
|Old Faithful||High 70|
Average September Precipitation
|Days of Precipitation||Total Precipitation||Total Snowfall|