Westport, South Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.2 °F (low) to 54.1 °F (high). Annual precipitation averages 22.3 Inches. Westport is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.8 °F | 21.3 °F | 0.43 in. |
| February | 6.2 °F | 26.6 °F | 0.55 in. |
| March | 18.5 °F | 39.2 °F | 0.95 in. |
| April | 31.6 °F | 54.8 °F | 1.82 in. |
| May | 44.7 °F | 67.8 °F | 3.34 in. |
| June | 55.6 °F | 77.4 °F | 3.74 in. |
| July | 60.0 °F | 82.6 °F | 3.68 in. |
| August | 57.2 °F | 81.2 °F | 2.4 in. |
| September | 47.8 °F | 72.9 °F | 2.2 in. |
| October | 34.2 °F | 57.9 °F | 1.89 in. |
| November | 20.4 °F | 40.5 °F | 0.71 in. |
| December | 8.5 °F | 26.6 °F | 0.57 in. |
| Annual | 32.2 °F | 54.1 °F | 22.28 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 4a : -30°F to -25°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |