Hartwell, Missouri has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.1 °C (low) to 19 °C (high). Annual precipitation averages 1105.4 Millimeters. Hartwell is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.3 °C | 4.6 °C | 43.18 mm |
| February | -4.2 °C | 7.4 °C | 50.29 mm |
| March | 0.9 °C | 13.3 °C | 72.39 mm |
| April | 6.4 °C | 19.1 °C | 116.84 mm |
| May | 12.7 °C | 24.2 °C | 142.75 mm |
| June | 18.1 °C | 29.1 °C | 132.84 mm |
| July | 20.2 °C | 31.7 °C | 117.35 mm |
| August | 19 °C | 31.2 °C | 102.36 mm |
| September | 14.1 °C | 26.9 °C | 110.74 mm |
| October | 7.3 °C | 20.7 °C | 87.38 mm |
| November | 1.2 °C | 13.1 °C | 74.68 mm |
| December | -3.8 °C | 6.8 °C | 54.61 mm |
| Annual | 7.1 °C | 19 °C | 1105.41 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |