| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 15°F | 35°F | 24°F | 0.7" |
| February | 23°F | 48°F | 35°F | 0.6" |
| March | 27°F | 55°F | 40°F | 0.8" |
| April | 32°F | 60°F | 45°F | 2.5" |
| May | 37°F | 64°F | 50°F | 3.5" |
| June | 47°F | 77°F | 62°F | 4.5" |
| July | 51°F | 86°F | 69°F | 2.5" |
| August | 49°F | 83°F | 66°F | 3.3" |
| September | 41°F | 71°F | 55°F | 4.6" |
| October | 35°F | 61°F | 47°F | 1.7" |
| November | 24°F | 47°F | 35°F | 1.4" |
| December | 12°F | 33°F | 22°F | 1.0" |
| Index | Fairfield | Montana | National |
| Air quality index | 21 | 34 | 42 |
| Pollution index | 260,100 | 834,473 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 350 |
| Days with moderate air quality | 12 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.004% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Sun River, MT | 41 | 21 | 58.0% |
| Choteau, MT | 1,878 | 21 | 58.0% |
| Fort Shaw, MT | 138 | 21 | 58.0% |
| Power, MT | 153 | 21 | 58.0% |
| Simms, MT | 338 | 21 | 58.0% |
| Fairfield, MT | 690 | 21 | 58.0% |
| City | Population | Air Quality Index | National Avg. |
| McRae, AR | 690 | 45 | 10.0% |
| Willow Valley, AZ | 690 | 13 | 74.0% |
| Wabasso, FL | 690 | 36 | 28.0% |
| Avon, IL | 690 | 41 | 18.0% |
| Beverly Shores, IN | 690 | 37 | 26.0% |
| Fairfield, MT | 690 | 21 | 58.0% |
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