Montana · county records since 1895, through September 2026.
Weather › Montana › Jefferson County
Jefferson County has warmed about 0.5° per decade since 1970. September 2026 averaged 52.9° there, right at the usual for September (41st warmest of 132).
That is the 1991 to 2020 average for these dates in Jefferson County. The Weather Service forecast fills in below.
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Each bar is a month's average temperature against the usual for that month (1991 to 2020). Ranks compare the same month in every year since 1895.
Rain and melted snow against the usual for each month. The drought reading is NOAA's Palmer index for the county.
| Month | Usual high / low | Usual rain | Warmest | Coldest |
|---|---|---|---|---|
| January | 33° / 15° | 0.9 in | 33.1° 1953 | -1.9° 1937 |
| February | 35° / 15° | 0.9 in | 34.4° 1961 | 5.7° 1936 |
| March | 43° / 22° | 1.2 in | 39.2° 1910 | 18.6° 1912 |
| April | 50° / 27° | 1.9 in | 45.2° 1910 | 27.7° 1975 |
| May | 59° / 35° | 2.5 in | 54.2° 1934 | 40.1° 1916 |
| June | 67° / 42° | 2.9 in | 62.3° 2021 | 47.2° 1901 |
| July | 78° / 49° | 1.4 in | 69.9° 2007 | 52.6° 1993 |
| August | 77° / 47° | 1.3 in | 66.6° 2022 | 55.2° 1907 |
| September | 66° / 40° | 1.3 in | 58.3° 1938 | 40.2° 1965 |
| October | 52° / 30° | 1.3 in | 47.1° 2015 | 30.8° 1919 |
| November | 39° / 21° | 1.1 in | 38.9° 1949 | 14.5° 1985 |
| December | 31° / 14° | 1.0 in | 32.3° 2025 | 8.1° 1983 |
Warmest and coldest are the month's whole-month average temperature, with the year it happened.