Three Forks, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.8 °C (low) to 14.7 °C (high). Annual precipitation averages 298 Millimeters. Three Forks is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.7 °C | 1.3 °C | 8.64 mm |
| February | -9.1 °C | 3.5 °C | 7.62 mm |
| March | -5.3 °C | 8.9 °C | 16 mm |
| April | -1.2 °C | 13.7 °C | 33.78 mm |
| May | 3.7 °C | 18.9 °C | 49.53 mm |
| June | 7.4 °C | 23.7 °C | 60.71 mm |
| July | 10.3 °C | 29.9 °C | 27.43 mm |
| August | 8.8 °C | 29.4 °C | 23.88 mm |
| September | 4.7 °C | 23.4 °C | 25.91 mm |
| October | -0.8 °C | 15.2 °C | 20.83 mm |
| November | -6.4 °C | 6.8 °C | 13.46 mm |
| December | -10.4 °C | 1.2 °C | 10.16 mm |
| Annual | -0.8 °C | 14.7 °C | 297.95 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |