Watertown, South Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 32.6 °F (low) to 53.4 °F (high). Annual precipitation averages 24 Inches. Watertown is located in USDA Plant Hardiness Zone 4b. 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 | 2.8 °F | 21.6 °F | 0.68 in. |
| February | 6.5 °F | 26.1 °F | 0.67 in. |
| March | 18.7 °F | 38.3 °F | 1.19 in. |
| April | 31.3 °F | 53.9 °F | 2.3 in. |
| May | 44.5 °F | 66.6 °F | 2.92 in. |
| June | 55.4 °F | 76.5 °F | 3.78 in. |
| July | 60.0 °F | 81.8 °F | 3.23 in. |
| August | 57.3 °F | 79.9 °F | 2.85 in. |
| September | 48.4 °F | 72.0 °F | 2.6 in. |
| October | 34.7 °F | 56.9 °F | 2.23 in. |
| November | 21.4 °F | 40.7 °F | 0.82 in. |
| December | 9.6 °F | 27.0 °F | 0.69 in. |
| Annual | 32.6 °F | 53.4 °F | 23.96 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 4b : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |