The highest day temperature in September 2025 was 75°F. The lowest night temperature was 37°F. The average values for day and night temperatures during September were 62.5°F и 44.4°F respectivly.

Most of the days in September are sunny but you can also expect cloudy and gloomy days.

Precipitation total in September for Yellowstone is 1.8 in. It makes september one of the least rainy months of the year.

The average wind speed in September is 6.7 mph. This value is relatively stable throughout the year.

We are using day length and cloud cover information for each day of the month to calculate averages for this chart. Average sunny hours for Yellowstone in September is 9.5 hours.