| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 30°F | 20°F | 1.5" |
| February | 10°F | 28°F | 18°F | 1.2" |
| March | 21°F | 45°F | 31°F | 2.1" |
| April | 30°F | 56°F | 42°F | 1.3" |
| May | 37°F | 63°F | 50°F | 5.0" |
| June | 46°F | 74°F | 59°F | 3.2" |
| July | 52°F | 84°F | 68°F | 2.0" |
| August | 51°F | 82°F | 66°F | 0.9" |
| September | 42°F | 69°F | 54°F | 7.8" |
| October | 35°F | 59°F | 45°F | 2.5" |
| November | 22°F | 42°F | 31°F | 1.5" |
| December | 12°F | 30°F | 21°F | 1.3" |
| Index | Simms | Montana | National |
| Air quality index | 21 | 34 | 42 |
| Pollution index | 1,148,190 | 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 | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Fort Shaw, MT | 138 | 21 | 58.0% |
| Sun River, MT | 41 | 21 | 58.0% |
| Fairfield, MT | 690 | 21 | 58.0% |
| Simms, MT | 338 | 21 | 58.0% |
| City | Population | Air Quality Index | National Avg. |
| Northway, AK | 338 | 38 | 24.0% |
| Tununak, AK | 338 | 31 | 38.0% |
| St. Charles, AR | 338 | 43 | 14.0% |
| Strawberry, AR | 338 | 45 | 10.0% |
| Winkelman, AZ | 338 | 47 | 6.0% |
| Simms, MT | 338 | 21 | 58.0% |
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