Bynum, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -0.8 °C (low) to 13 °C (high). Annual precipitation averages 334.8 Millimeters. Bynum is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.4 °C | 1.8 °C | 10.41 mm |
| February | -10 °C | 2.6 °C | 11.68 mm |
| March | -6.3 °C | 6.6 °C | 16 mm |
| April | -1.8 °C | 11.5 °C | 37.34 mm |
| May | 2.9 °C | 16.8 °C | 55.63 mm |
| June | 7 °C | 21 °C | 68.07 mm |
| July | 10.1 °C | 26.9 °C | 27.94 mm |
| August | 9.2 °C | 26.5 °C | 28.96 mm |
| September | 5 °C | 20.8 °C | 31.75 mm |
| October | -0.4 °C | 13.6 °C | 22.1 mm |
| November | -5.6 °C | 6.3 °C | 13.72 mm |
| December | -9.6 °C | 2.1 °C | 11.18 mm |
| Annual | -0.8 °C | 13 °C | 334.78 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 21 - May 31 |
| 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 |