| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 19°F | 28°F | 23°F | 4.8" |
| February | 19°F | 30°F | 24°F | 4.6" |
| March | 23°F | 34°F | 27°F | 6.5" |
| April | 27°F | 41°F | 32°F | 3.4" |
| May | 35°F | 52°F | 42°F | 2.7" |
| June | 42°F | 60°F | 49°F | 3.5" |
| July | 53°F | 72°F | 61°F | 1.0" |
| August | 51°F | 71°F | 59°F | 1.0" |
| September | 44°F | 61°F | 50°F | 1.6" |
| October | 32°F | 45°F | 37°F | 4.2" |
| November | 23°F | 33°F | 27°F | 6.4" |
| December | 16°F | 25°F | 21°F | 6.1" |
| Index | Plains | Montana | National |
| Air quality index | 40 | 34 | 42 |
| Pollution index | 1,107,360 | 834,473 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 224 |
| Days with moderate air quality | 137 |
| Days w/ poor A.Q. for sensitive groups | 3 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.004% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Weeksville, MT | 86 | 37 | 26.0% |
| Camas, MT | 89 | 37 | 26.0% |
| Hot Springs, MT | 627 | 37 | 26.0% |
| Paradise, MT | 114 | 40 | 20.0% |
| St. Regis, MT | 207 | 40 | 20.0% |
| Plains, MT | 1,019 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Leroy, AL | 1,019 | 42 | 16.0% |
| Hebron, MD | 1,019 | 36 | 28.0% |
| New Salem, ND | 1,019 | 36 | 28.0% |
| Cochranton, PA | 1,019 | 31 | 38.0% |
| Gilbert Creek, WV | 1,019 | 295 | 490.0% |
| Plains, MT | 1,019 | 40 | 20.0% |
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