Keystone weather in September 2025

Expect 23°C daytime maximum temperatures in the shade with on average 9 hours of sunshine per day in Keystone in September. Check more long-term weather averages for Keystone in September before you book your next holiday to South Dakota in 2025/2026.

  • 23°C maximum daytime temperature in September in Keystone23
    23°C max day temperature
  • 9 hours of sunshine per day
  • 8 days with some rainfall in September in Keystone8
    8 days with some rainfall
  • 6°C minimum night-time temperature in September in Keystone6
    6°C min night temperature
  • 12 hours of daylight per day in September in Keystone12
    12 hours of daylight per day
  • No heat & humidity in September in Keystone0
    No heat & humidity
  • 32 mm monthly rainfall in September in Keystone32
    32 mm of monthly rainfall
  • UV (maximum) index 6 (High) in September in Keystone6
    6 (High) UV index

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The September weather guide for South Dakota (Keystone) shows long term weather averages processed from data supplied by CRU (University of East Anglia), the Met Office & the Netherlands Meteorological Institute. Find out more about our data sources.

Metric (°C / mm)  |  Imperial (°F / inches)

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How hot is it in Keystone in September?

Daytime temperatures usually reach 23°C in Keystone in September, falling to 6°C at night.

How sunny is it in Keystone in September?

There are normally 9 hours of bright sunshine each day in Keystone in September - that's 68% of daylight hours.

Does it rain in Keystone in September?

There are usually 8 days with some rain in Keystone in September and the average monthly rainfall is 32mm.

Keystone September sunrise & sunset times

Browse the sunrise and sunset times for Keystone in September 2025. Select a month to view Keystone sunrise and sunset times for the next 12 months.

JanFebMarAprMayJunJulAugSepOctNovDec

Date Sunrise times Sunset times
Monday, 1st September 2025 05:17 18:29
Monday, 15th September 2025 05:33 18:03
Tuesday, 30th September 2025 05:51 17:36

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