Big Sandy, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -0.8 °C (low) to 14.4 °C (high). Annual precipitation averages 321.3 Millimeters. Big Sandy 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 | -13.4 °C | -0.6 °C | 12.19 mm |
| February | -11.9 °C | 1.7 °C | 9.65 mm |
| March | -6.7 °C | 7.3 °C | 12.45 mm |
| April | -0.8 °C | 14.6 °C | 29.46 mm |
| May | 4.5 °C | 19.7 °C | 45.97 mm |
| June | 9.2 °C | 24.3 °C | 74.68 mm |
| July | 12.1 °C | 30.1 °C | 36.32 mm |
| August | 10.9 °C | 29.8 °C | 25.65 mm |
| September | 5.8 °C | 23.7 °C | 26.42 mm |
| October | -0.6 °C | 15.3 °C | 22.35 mm |
| November | -6.8 °C | 6.4 °C | 14.99 mm |
| December | -11.9 °C | 0.8 °C | 11.18 mm |
| Annual | -0.8 °C | 14.4 °C | 321.31 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 |