Custer, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 1 °C (low) to 16.1 °C (high). Annual precipitation averages 355.1 Millimeters. 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 | -10.9 °C | 1.7 °C | 12.95 mm |
| February | -9.6 °C | 3.9 °C | 11.43 mm |
| March | -4.8 °C | 10.3 °C | 21.84 mm |
| April | 0.3 °C | 15.7 °C | 37.34 mm |
| May | 5.8 °C | 20.7 °C | 53.09 mm |
| June | 10.9 °C | 26.1 °C | 63.5 mm |
| July | 14.2 °C | 31.2 °C | 38.61 mm |
| August | 12.9 °C | 30.9 °C | 23.37 mm |
| September | 7.6 °C | 25.1 °C | 27.18 mm |
| October | 0.8 °C | 16.6 °C | 38.1 mm |
| November | -5.2 °C | 8.7 °C | 16 mm |
| December | -10.1 °C | 2.7 °C | 11.68 mm |
| Annual | 1 °C | 16.1 °C | 355.09 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 4a : -34.4°C to -31.7°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |