Three Forks, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30.7 °F (low) to 58.4 °F (high). Annual precipitation averages 11.7 Inches. 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 | 12.7 °F | 34.3 °F | 0.34 in. |
| February | 15.7 °F | 38.3 °F | 0.3 in. |
| March | 22.5 °F | 48.0 °F | 0.63 in. |
| April | 29.8 °F | 56.6 °F | 1.33 in. |
| May | 38.6 °F | 66.0 °F | 1.95 in. |
| June | 45.4 °F | 74.6 °F | 2.39 in. |
| July | 50.6 °F | 85.8 °F | 1.08 in. |
| August | 47.9 °F | 85.0 °F | 0.94 in. |
| September | 40.4 °F | 74.1 °F | 1.02 in. |
| October | 30.5 °F | 59.3 °F | 0.82 in. |
| November | 20.5 °F | 44.2 °F | 0.53 in. |
| December | 13.2 °F | 34.1 °F | 0.4 in. |
| Annual | 30.7 °F | 58.4 °F | 11.73 in. |
| 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 : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |