| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 16°F | 34°F | 25°F | 0.9" |
| February | 21°F | 40°F | 30°F | 1.0" |
| March | 26°F | 51°F | 38°F | 1.0" |
| April | 31°F | 60°F | 44°F | 1.1" |
| May | 38°F | 69°F | 53°F | 1.4" |
| June | 45°F | 78°F | 61°F | 2.0" |
| July | 51°F | 91°F | 71°F | 0.6" |
| August | 49°F | 88°F | 68°F | 0.7" |
| September | 42°F | 77°F | 58°F | 1.0" |
| October | 33°F | 59°F | 45°F | 1.2" |
| November | 24°F | 44°F | 33°F | 1.4" |
| December | 15°F | 32°F | 24°F | 1.2" |
| Index | Corvallis | Montana | National |
| Air quality index | 40 | 34 | 42 |
| Pollution index | 848,303 | 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 | 0.000% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Victor, MT | 973 | 40 | 20.0% |
| Hamilton, MT | 4,827 | 40 | 20.0% |
| Charlos Heights, MT | 0 | 40 | 20.0% |
| Pinesdale, MT | 999 | 40 | 20.0% |
| Stevensville, MT | 1,897 | 40 | 20.0% |
| Corvallis, MT | 1,755 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Kaibito, AZ | 1,755 | 45 | 10.0% |
| Portola, CA | 1,755 | 44 | 12.0% |
| Prudenville, MI | 1,755 | 36 | 28.0% |
| Decatur, MS | 1,755 | 36 | 28.0% |
| Mercer, PA | 1,755 | 31 | 38.0% |
| Corvallis, MT | 1,755 | 40 | 20.0% |
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