Sun River, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 0.3 °C (low) to 14.7 °C (high). Annual precipitation averages 326.9 Millimeters. Sun River is located in USDA Plant Hardiness Zone 4a. 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 | -9.6 °C | 2.5 °C | 9.65 mm |
| February | -8.9 °C | 3.7 °C | 11.94 mm |
| March | -5.3 °C | 8.2 °C | 14.22 mm |
| April | -0.7 °C | 13.7 °C | 39.12 mm |
| May | 4.1 °C | 18.8 °C | 51.56 mm |
| June | 8.3 °C | 23.2 °C | 69.34 mm |
| July | 11.1 °C | 29.3 °C | 27.94 mm |
| August | 10.3 °C | 28.7 °C | 28.19 mm |
| September | 6.2 °C | 22.9 °C | 29.72 mm |
| October | 1 °C | 15.2 °C | 21.84 mm |
| November | -4.3 °C | 7.6 °C | 13.72 mm |
| December | -8.5 °C | 2.8 °C | 9.65 mm |
| Annual | 0.3 °C | 14.7 °C | 326.89 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 4a : -34.4°C to -31.7°C |
| Plant Hardiness Zone - 2012 | Zone 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |