Sedan, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 28.1 °F (low) to 54.3 °F (high). Annual precipitation averages 23.5 Inches. Sedan is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around Jun. 11 - Jun. 20 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 13.6 °F | 34.5 °F | 1.33 in. |
| February | 14.2 °F | 35.7 °F | 1.28 in. |
| March | 20.5 °F | 43.4 °F | 1.52 in. |
| April | 26.0 °F | 51.4 °F | 2.74 in. |
| May | 33.4 °F | 60.1 °F | 3.17 in. |
| June | 40.2 °F | 69.0 °F | 3.54 in. |
| July | 45.0 °F | 80.0 °F | 1.66 in. |
| August | 43.5 °F | 79.6 °F | 1.49 in. |
| September | 37.5 °F | 69.1 °F | 1.76 in. |
| October | 29.2 °F | 54.4 °F | 1.89 in. |
| November | 20.3 °F | 41.7 °F | 1.6 in. |
| December | 13.6 °F | 32.9 °F | 1.52 in. |
| Annual | 28.1 °F | 54.3 °F | 23.5 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | Jun. 11 - Jun. 20 |
| Average Days With Frost | Over 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 | Severe Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |