Zortman, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Annual precipitation averages 508.8 Millimeters. Zortman 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.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.2 °C | 0.7 °C | 17.78 mm |
| February | -10 °C | 1.3 °C | 16.76 mm |
| March | -6 °C | 5.6 °C | 22.1 mm |
| April | -1.5 °C | 10.7 °C | 46.23 mm |
| May | 3.6 °C | 15.9 °C | 83.82 mm |
| June | 8.4 °C | 20.9 °C | 111 mm |
| July | 11.9 °C | 26.7 °C | 46.99 mm |
| August | 11.3 °C | 26.4 °C | 45.21 mm |
| September | 6.3 °C | 20.1 °C | 44.7 mm |
| October | 0.1 °C | 12.2 °C | 35.56 mm |
| November | -4.9 °C | 5.7 °C | 21.08 mm |
| December | -9.3 °C | 1.3 °C | 17.53 mm |
| Annual | -0 °C | 12.3 °C | 508.76 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |