| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 9°F | 33°F | 20°F | 0.4" |
| February | 12°F | 37°F | 23°F | 0.4" |
| March | 20°F | 44°F | 31°F | 0.6" |
| April | 26°F | 52°F | 38°F | 1.4" |
| May | 34°F | 62°F | 47°F | 2.2" |
| June | 41°F | 71°F | 55°F | 2.8" |
| July | 46°F | 84°F | 65°F | 1.0" |
| August | 43°F | 80°F | 61°F | 1.2" |
| September | 36°F | 71°F | 52°F | 1.3" |
| October | 28°F | 54°F | 39°F | 1.4" |
| November | 19°F | 42°F | 30°F | 0.5" |
| December | 7°F | 29°F | 17°F | 0.5" |
| Index | Boulder | Montana | National |
| Air quality index | 40 | 34 | 42 |
| Pollution index | 568,053 | 834,473 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 288 |
| Days with moderate air quality | 75 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.003% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Jefferson City, MT | 596 | 40 | 20.0% |
| Basin, MT | 267 | 40 | 20.0% |
| Elkhorn, MT | 0 | 40 | 20.0% |
| Clancy, MT | 1,964 | 40 | 20.0% |
| Boulder, MT | 1,027 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Glidden, IA | 1,027 | 37 | 26.0% |
| Monroe City, IN | 1,027 | 36 | 28.0% |
| Barataria, LA | 1,027 | 45 | 10.0% |
| Belgrade, MN | 1,027 | 32 | 36.0% |
| Walnut Grove, MS | 1,027 | 36 | 28.0% |
| Boulder, MT | 1,027 | 40 | 20.0% |
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