September in Yellowstone National Park is a best window month: highs around 66°F, lows around 36°F. Crowds: moderate — #4 busiest of the park's 12 months. Elk rut echoes through the valleys; crowds thin, mornings crisp. The editorial best window here is June & September. You get about 12h 31m of daylight. To finish Mount Washburn (2h 45m) before dark, leave the trailhead by about 4:46 PM.
Month data reviewed · how we check this
| Verdict | Best window The editorial pick — weather, access and experience line up. |
|---|---|
| Temps °F | 66° high / 36° low |
| Crowds | moderate · #4 busiest of the park's 12 months |
| What September is like | Elk rut echoes through the valleys; crowds thin, mornings crisp |
| Best window (whole year) | June & September |
| Peak crowds (whole year) | Jul–Aug |
CROWDS: RELATIVE SEASONALITY FROM NPS VISITATION STATISTICS · TEMPS: APPROXIMATE NOAA NORMALS AT MAIN VISITOR ELEVATION — HIGH COUNTRY RUNS 10–20°F COLDER
DAYLIGHT ON SEPTEMBER 15 · LOCAL PARK TIME (MDT)COMPUTED FROM THE PARK'S OWN COORDINATES FOR THE 15TH — THE MIDDLE OF THE MONTH STANDS FOR IT, AS IT DOES FOR CLIMATE NORMALS. WITHIN A MONTH THESE TIMES SHIFT BY UP TO AN HOUR
LEAVE THE TRAILHEAD BY — TO FINISH BEFORE DARK ON SEPTEMBER 15WALKING TIMES ESTIMATED FROM EACH TRAIL'S MEASURED DISTANCE AND ELEVATION GAIN — A PLANNING FIGURE, NOT A PACE. ADD YOUR OWN MARGIN FOR PHOTOS, REST AND CROWDS. WATER AT THE COOL-WEATHER RATE, BECAUSE THIS MONTH AVERAGES 66°F. TRAILS WE HAVE NOT MEASURED ARE LEFT OUT RATHER THAN GUESSED
WHAT SEPTEMBER ASKS OF YOU HEREYellowstone National Park in October — Shoulder, highs around 52°F, crowds: quiet (roads begin closing for winter; snow arrives early).
Our verdict for September is "Best window". The editorial pick — weather, access and experience line up. Expect highs around 66°F and lows around 36°F, with crowds at the "moderate" level. Temperatures are approximate NOAA normals at the main visitor elevation; crowd levels follow published NPS visitation statistics.
Across the full 12-month review, the best window is June & September, and the peak-crowd months are Jul–Aug. September itself we rate "Best window".
October we rate "Shoulder" against "Best window" for September, with highs around 52°F and crowds at the "quiet" level.
About 12h 31m on September 15: the sun rises around 7:01 AM and sets around 7:32 PM local park time (MDT). Computed from the park's own coordinates, so it is the light you actually get at the trailhead, not the nearest city's.
Mount Washburn takes about 2h 45m of walking, so on September 15 you would need to leave the trailhead by about 4:46 PM to finish before dark — the sun sets around 7:32 PM local park time (MDT). Walking times are estimated from each trail's measured distance and elevation gain, so treat them as a planning figure and add your own margin for photos, rest and crowds.
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