| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 36°F | 25°F | 0.6" |
| February | 15°F | 38°F | 25°F | 0.5" |
| March | 24°F | 48°F | 34°F | 0.8" |
| April | 29°F | 55°F | 41°F | 2.0" |
| May | 37°F | 64°F | 50°F | 3.5" |
| June | 45°F | 73°F | 59°F | 3.4" |
| July | 52°F | 85°F | 69°F | 1.5" |
| August | 50°F | 83°F | 66°F | 1.8" |
| September | 42°F | 73°F | 56°F | 1.5" |
| October | 33°F | 59°F | 44°F | 1.7" |
| November | 22°F | 46°F | 33°F | 0.8" |
| December | 12°F | 34°F | 23°F | 0.5" |
| Index | Lewistown | Montana | National |
| Air quality index | 21 | 34 | 42 |
| Pollution index | 263,666 | 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 | 0.005% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Lewistown Heights, MT | 312 | 21 | 58.0% |
| Moore, MT | 187 | 21 | 58.0% |
| Lewistown, MT | 5,923 | 21 | 58.0% |
| City | Population | Air Quality Index | National Avg. |
| Selinsgrove, PA | 5,923 | 35 | 30.0% |
| Woods Creek, WA | 5,922 | 45 | 10.0% |
| Old Tappan, NJ | 5,924 | 51 | 2.0% |
| Margate City, NJ | 5,921 | 37 | 26.0% |
| Oxford, MA | 5,926 | 40 | 20.0% |
| Lewistown, MT | 5,923 | 21 | 58.0% |
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