15. Montpelier, Vermont
> Average temperature, September 2021: 61.1°F (5.8°F above average)
> Average September temperature, 1901-2000: 55.3°F
> Hottest September on record: 1961 (63.1°F)
> Coldest September on record: 1950 (50.8°F)
14. Billings, Montana
> Average temperature, September 2021: 65.2°F (5.8°F above average)
> Average September temperature, 1901-2000: 59.4°F
> Hottest September on record: 2009 (66.7°F)
> Coldest September on record: 1965 (47.0°F)
13. Sheridan, Wyoming
> Average temperature, September 2021: 62.9°F (5.9°F above average)
> Average September temperature, 1901-2000: 57.0°F
> Hottest September on record: 1963 (64.3°F)
> Coldest September on record: 1965 (47.2°F)
12. Wausau, Wisconsin
> Average temperature, September 2021: 63.3°F (6.0°F above average)
> Average September temperature, 1901-2000: 57.3°F
> Hottest September on record: 2015 (64.9°F)
> Coldest September on record: 1993 (52.0°F)
11. Bismarck, North Dakota
> Average temperature, September 2021: 65.1°F (6.2°F above average)
> Average September temperature, 1901-2000: 58.9°F
> Hottest September on record: 1948 (66.1°F)
> Coldest September on record: 1965 (47.9°F)