Middletown, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.7 °C (low) to 17.2 °C (high). Annual precipitation averages 978.7 Millimeters. Middletown is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.9 °C | 1.4 °C | 53.85 mm |
| February | -6.1 °C | 4.1 °C | 47.5 mm |
| March | -0.8 °C | 10.7 °C | 65.28 mm |
| April | 5.2 °C | 18 °C | 99.06 mm |
| May | 11.6 °C | 23.6 °C | 114.3 mm |
| June | 16.7 °C | 28.4 °C | 114.81 mm |
| July | 18.4 °C | 29.9 °C | 103.89 mm |
| August | 17.2 °C | 29.2 °C | 89.15 mm |
| September | 12.6 °C | 26.3 °C | 82.8 mm |
| October | 6.1 °C | 19.3 °C | 79.5 mm |
| November | 0.1 °C | 11 °C | 72.39 mm |
| December | -4.8 °C | 4.2 °C | 56.13 mm |
| Annual | 5.7 °C | 17.2 °C | 978.66 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| 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 |