| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 13°F | 35°F | 24°F | 0.6" |
| February | 18°F | 41°F | 28°F | 0.7" |
| March | 25°F | 52°F | 38°F | 0.5" |
| April | 31°F | 60°F | 44°F | 0.9" |
| May | 39°F | 69°F | 53°F | 1.8" |
| June | 47°F | 79°F | 63°F | 2.0" |
| July | 55°F | 91°F | 73°F | 0.7" |
| August | 52°F | 88°F | 69°F | 1.1" |
| September | 44°F | 77°F | 59°F | 1.1" |
| October | 34°F | 62°F | 46°F | 0.8" |
| November | 23°F | 47°F | 34°F | 0.8" |
| December | 12°F | 33°F | 22°F | 0.8" |
| Index | West | Helena | Montana |
| Air quality index | 40 | 40 | 34 |
| Pollution index | 1,148,190 | 1,148,190 | 834,473 |
| 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 | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Montana City, MT | 2,821 | 40 | 20.0% |
| Helena Valley Northwest, MT | 4,256 | 40 | 20.0% |
| Marysville, MT | 71 | 40 | 20.0% |
| Spokane Creek, MT | 438 | 40 | 20.0% |
| Helena Valley Southeast, MT | 8,546 | 40 | 20.0% |
| Helena, MT | 32,655 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Orangeville, ON | 32,668 | n/a | |
| Matthews, NC | 32,682 | 49 | 2.0% |
| Uniondale, NY | 32,621 | 51 | 2.0% |
| St. Charles, IL | 32,612 | 55 | 10.0% |
| Florence, KY | 32,721 | 54 | 8.0% |
| Helena, MT | 32,655 | 40 | 20.0% |
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