The highest day temperature in September 2025 was 89°F. The lowest night temperature was 41°F. The average values for day and night temperatures during September were 76.7°F и 57.6°F respectivly.

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

Precipitation total in September for Spearfish is 0.2 in. It makes september one of the least rainy months of the year.

The average wind speed in September is 8.0 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 Spearfish in September is 10.3 hours.