Winston, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -0.1 °C (low) to 13.6 °C (high). Annual precipitation averages 328.9 Millimeters. Winston is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.5 °C | 1.2 °C | 10.92 mm |
| February | -8.6 °C | 2.9 °C | 9.65 mm |
| March | -4.9 °C | 7.9 °C | 17.02 mm |
| April | -1.1 °C | 12.7 °C | 34.29 mm |
| May | 3.5 °C | 17.7 °C | 53.34 mm |
| June | 7.4 °C | 22.4 °C | 64.01 mm |
| July | 10.7 °C | 28.3 °C | 32.51 mm |
| August | 9.7 °C | 27.9 °C | 28.7 mm |
| September | 5.7 °C | 22 °C | 27.94 mm |
| October | 0.2 °C | 13.9 °C | 23.11 mm |
| November | -5.1 °C | 5.8 °C | 15.24 mm |
| December | -9.2 °C | 0.9 °C | 12.19 mm |
| Annual | -0.1 °C | 13.6 °C | 328.92 mm |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |