September weather in Boulder, MT
The average temperature in Boulder in September is 55.0°F (38.1°F–71.9°F). Average precipitation: 1.10 inches.
September is a fall month in Boulder, and is warmer than the annual average of 42.6°F. Daily temperatures swing about 33.8°F between overnight low and afternoon high. Expect about 7 days with precipitation. Daylight averages about 12h 19m. For travel, September is a comfortable month to visit.
Avg High
71.9°F
Avg Low
38.1°F
Precipitation
1.10 in
Daylight
12h 19m
September records in Boulder
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| September 1 | 93.0°F (1955) | 25.0°F (2006) | 0.87 in (1963) |
| September 2 | 91.9°F (1950) | 26.1°F (1974) | 0.36 in (1963) |
| September 3 | 93.0°F (1950) | 27.0°F (1958) | 0.20 in (1971) |
| September 4 | 95.0°F (2022) | 25.0°F (1962) | 0.23 in (1960) |
| September 5 | 95.0°F (2020) | 24.1°F (1969) | 0.35 in (2016) |
| September 6 | 96.1°F (2022) | 27.0°F (1956) | 0.87 in (2001) |
| September 7 | 95.0°F (2022) | 18.0°F (1992) | 0.75 in (2020) |
| September 8 | 93.0°F (2022) | 19.9°F (1960) | 1.18 in (1995) |
| September 9 | 90.0°F (1979) | 19.0°F (1962) | 0.59 in (1998) |
| September 10 | 90.0°F (1979) | 25.0°F (1983) | 0.50 in (1961) |
| September 11 | 86.0°F (1954) | 16.0°F (1989) | 0.89 in (1991) |
| September 12 | 88.0°F (1981) | 18.0°F (1989) | 0.82 in (1985) |
| September 13 | 89.1°F (1948) | 21.0°F (1974) | 0.39 in (1982) |
| September 14 | 89.1°F (1948) | 16.0°F (1970) | 0.29 in (1986) |
| September 15 | 90.0°F (2000) | 17.1°F (1970) | 0.90 in (2025) |
| September 16 | 91.9°F (2000) | 19.9°F (1965) | 0.67 in (2015) |
| September 17 | 87.1°F (1981) | 8.1°F (1965) | 0.57 in (1977) |
| September 18 | 89.1°F (1981) | 10.0°F (1965) | 0.85 in (1989) |
| September 19 | 89.1°F (1981) | 18.0°F (1964) | 0.48 in (2004) |
| September 20 | 89.1°F (1949) | 15.1°F (1983) | 0.78 in (1968) |
| September 21 | 86.0°F (1966) | 16.0°F (1995) | 0.28 in (1962) |
| September 22 | 84.0°F (1966) | 16.0°F (1960) | 0.52 in (2016) |
| September 23 | 86.0°F (1966) | 17.1°F (1996) | 0.50 in (2022) |
| September 24 | 86.0°F (1994) | 16.0°F (2000) | 0.37 in (2005) |
| September 25 | 87.1°F (1963) | 17.1°F (1970) | 0.61 in (1981) |
| September 26 | 86.0°F (2024) | 19.0°F (1972) | 0.76 in (2013) |
| September 27 | 84.9°F (1963) | 16.0°F (1961) | 0.50 in (2014) |
| September 28 | 87.1°F (1967) | 17.1°F (1999) | 0.25 in (1965) |
| September 29 | 87.1°F (1967) | 10.9°F (1985) | 0.32 in (2007) |
| September 30 | 86.0°F (1967) | 14.0°F (1985) | 0.80 in (2022) |