Sinai, South Dakota has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 34 °F (low) to 54.5 °F (high). Annual precipitation averages 26.4 Inches. Sinai 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 | 5.0 °F | 23.1 °F | 0.58 in. |
| February | 9.3 °F | 28.0 °F | 0.71 in. |
| March | 20.7 °F | 40.0 °F | 1.22 in. |
| April | 32.9 °F | 55.0 °F | 2.56 in. |
| May | 45.6 °F | 67.5 °F | 3.65 in. |
| June | 56.4 °F | 77.4 °F | 4.21 in. |
| July | 60.6 °F | 82.1 °F | 3.42 in. |
| August | 58.3 °F | 79.6 °F | 3.22 in. |
| September | 49.7 °F | 72.6 °F | 2.89 in. |
| October | 36.0 °F | 58.4 °F | 2.12 in. |
| November | 22.7 °F | 41.8 °F | 0.99 in. |
| December | 11.0 °F | 28.1 °F | 0.78 in. |
| Annual | 34 °F | 54.5 °F | 26.35 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 | Severe Drought |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |