Custer, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 33.8 °F (low) to 61.1 °F (high). Annual precipitation averages 14 Inches. Custer 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 | 12.3 °F | 35.1 °F | 0.51 in. |
| February | 14.8 °F | 39.1 °F | 0.45 in. |
| March | 23.4 °F | 50.5 °F | 0.86 in. |
| April | 32.6 °F | 60.2 °F | 1.47 in. |
| May | 42.5 °F | 69.3 °F | 2.09 in. |
| June | 51.6 °F | 79.0 °F | 2.5 in. |
| July | 57.5 °F | 88.2 °F | 1.52 in. |
| August | 55.3 °F | 87.7 °F | 0.92 in. |
| September | 45.7 °F | 77.1 °F | 1.07 in. |
| October | 33.4 °F | 61.9 °F | 1.5 in. |
| November | 22.7 °F | 47.7 °F | 0.63 in. |
| December | 13.8 °F | 36.9 °F | 0.46 in. |
| Annual | 33.8 °F | 61.1 °F | 13.98 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 4a : -30°F to -25°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |