| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 19°F | 31°F | 25°F | 1.6" |
| February | 21°F | 35°F | 27°F | 1.3" |
| March | 26°F | 46°F | 36°F | 2.5" |
| April | 30°F | 55°F | 43°F | 2.4" |
| May | 37°F | 64°F | 51°F | 4.2" |
| June | 45°F | 71°F | 59°F | 3.0" |
| July | 50°F | 85°F | 68°F | 4.1" |
| August | 46°F | 82°F | 65°F | 4.6" |
| September | 40°F | 73°F | 57°F | 6.3" |
| October | 33°F | 55°F | 44°F | 3.0" |
| November | 24°F | 39°F | 31°F | 2.0" |
| December | 15°F | 28°F | 21°F | 1.8" |
| Index | Darby | 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. |
| Sula, MT | 77 | 20 | 60.0% |
| Conner, MT | 95 | 40 | 20.0% |
| Charlos Heights, MT | 0 | 40 | 20.0% |
| Darby, MT | 685 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| Green Mountain Falls, CO | 685 | 45 | 10.0% |
| Cordova, IL | 685 | 42 | 16.0% |
| Maple Rapids, MI | 685 | 36 | 28.0% |
| Sycamore Hills, MO | 685 | 54 | 8.0% |
| Mott, ND | 685 | 33 | 34.0% |
| Darby, MT | 685 | 40 | 20.0% |
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