Thief River Falls, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1.8 °C (low) to 9.3 °C (high). Annual precipitation averages 600.2 Millimeters. Thief River Falls is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -20 °C | -9.9 °C | 17.02 mm |
| February | -18.3 °C | -7.3 °C | 15.24 mm |
| March | -10.4 °C | 0.4 °C | 20.07 mm |
| April | -1.7 °C | 10 °C | 32.51 mm |
| May | 5.5 °C | 18.1 °C | 78.49 mm |
| June | 11.9 °C | 23.3 °C | 100.33 mm |
| July | 13.6 °C | 25.7 °C | 92.71 mm |
| August | 12.2 °C | 25.3 °C | 75.95 mm |
| September | 7.2 °C | 20.1 °C | 71.88 mm |
| October | 0.6 °C | 11.3 °C | 52.83 mm |
| November | -7.5 °C | 1.4 °C | 23.11 mm |
| December | -15.2 °C | -6.4 °C | 20.07 mm |
| Annual | -1.8 °C | 9.3 °C | 600.21 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -34.4°C to -31.7°C |
| Plant Hardiness Zone - 2012 | Zone 3b : -37.2°C to -34.4°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |