| 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 | Lewis And Clark | Missoula | Montana |
| Air quality index | 40 | 40 | 34 |
| Pollution index | 848,303 | 848,303 | 834,473 |
| 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. |
| Florence, MT | 805 | 40 | 20.0% |
| Evaro, MT | 401 | 40 | 20.0% |
| Turah, MT | 309 | 40 | 20.0% |
| Lolo, MT | 4,064 | 40 | 20.0% |
| Frenchtown, MT | 1,741 | 40 | 20.0% |
| Missoula, MT | 74,994 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Union City, CA | 75,067 | 43 | 14.0% |
| Arlington Heights, IL | 75,071 | 55 | 10.0% |
| Milpitas, CA | 75,182 | 43 | 14.0% |
| Missouri City, TX | 75,348 | 52 | 4.0% |
| St. Joseph, MO | 75,369 | 43 | 14.0% |
| Missoula, MT | 74,994 | 40 | 20.0% |
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