Grass Range, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 32.5 °F (low) to 57.8 °F (high). Annual precipitation averages 17.4 Inches. Grass Range 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 | 13.5 °F | 35.4 °F | 0.55 in. |
| February | 15.0 °F | 37.4 °F | 0.5 in. |
| March | 22.6 °F | 46.4 °F | 0.86 in. |
| April | 30.5 °F | 55.8 °F | 1.71 in. |
| May | 39.7 °F | 64.9 °F | 3.31 in. |
| June | 47.9 °F | 73.5 °F | 3.27 in. |
| July | 54.1 °F | 83.6 °F | 1.81 in. |
| August | 52.5 °F | 83.3 °F | 1.46 in. |
| September | 43.6 °F | 72.7 °F | 1.43 in. |
| October | 33.2 °F | 58.8 °F | 1.14 in. |
| November | 22.5 °F | 45.6 °F | 0.73 in. |
| December | 14.7 °F | 36.3 °F | 0.6 in. |
| Annual | 32.5 °F | 57.8 °F | 17.37 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 | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |