| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 14°F | 36°F | 25°F | 1.5" |
| February | 19°F | 42°F | 29°F | 0.4" |
| March | 25°F | 52°F | 37°F | 1.2" |
| April | 28°F | 57°F | 41°F | 1.7" |
| May | 38°F | 62°F | 50°F | 3.7" |
| June | 47°F | 74°F | 60°F | 3.9" |
| July | 52°F | 87°F | 70°F | 2.9" |
| August | 50°F | 85°F | 67°F | 2.9" |
| September | 42°F | 72°F | 56°F | 4.7" |
| October | 34°F | 61°F | 46°F | 3.0" |
| November | 23°F | 46°F | 33°F | 2.7" |
| December | 15°F | 34°F | 23°F | 1.1" |
| Index | Harlowton | Montana | National |
| Air quality index | 21 | 34 | 42 |
| Pollution index | 133,005 | 834,473 | 2,726,193 |
| Measurement | Total |
| Days measured | 362 |
| Days with good air quality | 357 |
| Days with moderate air quality | 4 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.002% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.000% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Harlowton, MT | 1,031 | 21 | 58.0% |
| City | Population | Air Quality Index | National Avg. |
| Plymouth, CA | 1,031 | 52 | 4.0% |
| South Woodstock, CT | 1,031 | 33 | 34.0% |
| Shipshewana, IN | 1,031 | 37 | 26.0% |
| Bude, MS | 1,031 | 44 | 12.0% |
| Hillburn, NY | 1,031 | 51 | 2.0% |
| Harlowton, MT | 1,031 | 21 | 58.0% |
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