| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 0°F | 17°F | 8°F | 1.0" |
| February | 1°F | 19°F | 9°F | 1.1" |
| March | 18°F | 35°F | 26°F | 2.6" |
| April | 32°F | 52°F | 41°F | 2.4" |
| May | 44°F | 66°F | 54°F | 3.9" |
| June | 54°F | 75°F | 64°F | 4.8" |
| July | 58°F | 80°F | 69°F | 4.8" |
| August | 55°F | 78°F | 66°F | 4.9" |
| September | 48°F | 70°F | 58°F | 5.7" |
| October | 36°F | 55°F | 44°F | 3.8" |
| November | 22°F | 38°F | 29°F | 1.5" |
| December | 4°F | 20°F | 12°F | 0.8" |
| Index | Thief River Falls | Minnesota | National |
| Air quality index | 33 | 35 | 42 |
| Pollution index | 466,579 | 1,854,519 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 327 |
| Days with moderate air quality | 34 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.001% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| St. Hilaire, MN | 259 | 33 | 34.0% |
| Viking, MN | 139 | 33 | 34.0% |
| Holt, MN | 85 | 33 | 34.0% |
| Plummer, MN | 288 | 33 | 34.0% |
| Thief River Falls, MN | 9,032 | 33 | 34.0% |
| City | Population | Air Quality Index | National Avg. |
| Kulpsville, PA | 9,031 | 51 | 2.0% |
| Matawan, NJ | 9,033 | 51 | 2.0% |
| Sandpoint, ID | 9,030 | 43 | 14.0% |
| Oxford, NC | 9,027 | 44 | 12.0% |
| Ridgefield, WA | 9,027 | 38 | 24.0% |
| Thief River Falls, MN | 9,032 | 33 | 34.0% |