Ennis, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -0.9 °C (low) to 14 °C (high). Annual precipitation averages 338.3 Millimeters. Ennis is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Jun. 1 - Jun. 10 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.9 °C | 1.8 °C | 11.68 mm |
| February | -8.8 °C | 3.2 °C | 13.21 mm |
| March | -5.1 °C | 8.1 °C | 21.34 mm |
| April | -1.8 °C | 12.5 °C | 37.85 mm |
| May | 2.4 °C | 17.7 °C | 51.31 mm |
| June | 5.9 °C | 22.7 °C | 58.93 mm |
| July | 8.9 °C | 28.8 °C | 31.24 mm |
| August | 8 °C | 28.3 °C | 25.4 mm |
| September | 4.2 °C | 22.6 °C | 25.65 mm |
| October | -0.7 °C | 14.6 °C | 30.73 mm |
| November | -5.3 °C | 6.5 °C | 17.27 mm |
| December | -9.4 °C | 1.4 °C | 13.72 mm |
| Annual | -0.9 °C | 14 °C | 338.33 mm |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | Jun. 1 - Jun. 10 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |