Grass Range, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 0.3 °C (low) to 14.4 °C (high). Annual precipitation averages 441.2 Millimeters. 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 | -10.3 °C | 1.9 °C | 13.97 mm |
| February | -9.4 °C | 3 °C | 12.7 mm |
| March | -5.2 °C | 8 °C | 21.84 mm |
| April | -0.8 °C | 13.2 °C | 43.43 mm |
| May | 4.3 °C | 18.3 °C | 84.07 mm |
| June | 8.8 °C | 23.1 °C | 83.06 mm |
| July | 12.3 °C | 28.7 °C | 45.97 mm |
| August | 11.4 °C | 28.5 °C | 37.08 mm |
| September | 6.4 °C | 22.6 °C | 36.32 mm |
| October | 0.7 °C | 14.9 °C | 28.96 mm |
| November | -5.3 °C | 7.6 °C | 18.54 mm |
| December | -9.6 °C | 2.4 °C | 15.24 mm |
| Annual | 0.3 °C | 14.4 °C | 441.18 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 | Abnormally Dry |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |