Thorntown, Indiana has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.6 °C (low) to 16.5 °C (high). Annual precipitation averages 1069.6 Millimeters. Thorntown is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.3 °C | 1.3 °C | 71.88 mm |
| February | -5.8 °C | 3.6 °C | 56.64 mm |
| March | -0.9 °C | 9.7 °C | 76.2 mm |
| April | 5 °C | 16.9 °C | 107.19 mm |
| May | 11.2 °C | 22.8 °C | 112.01 mm |
| June | 16.1 °C | 27.3 °C | 128.52 mm |
| July | 17.8 °C | 28.9 °C | 114.55 mm |
| August | 16.7 °C | 28.3 °C | 88.65 mm |
| September | 12.4 °C | 25.6 °C | 78.99 mm |
| October | 6.2 °C | 18.8 °C | 80.52 mm |
| November | 0.5 °C | 10.6 °C | 83.31 mm |
| December | -4.3 °C | 4 °C | 71.12 mm |
| Annual | 5.6 °C | 16.5 °C | 1069.58 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |