Merrillville, Indiana has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 15.6 °C (high). Annual precipitation averages 1028.2 Millimeters. Merrillville 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 | -8.2 °C | 0.2 °C | 59.18 mm |
| February | -6.7 °C | 2.3 °C | 51.82 mm |
| March | -1.9 °C | 8.3 °C | 60.2 mm |
| April | 3.7 °C | 15.6 °C | 92.96 mm |
| May | 9.7 °C | 21.6 °C | 108.97 mm |
| June | 15.2 °C | 26.9 °C | 119.13 mm |
| July | 17.7 °C | 28.8 °C | 109.47 mm |
| August | 16.8 °C | 27.9 °C | 114.05 mm |
| September | 12.5 °C | 24.8 °C | 88.39 mm |
| October | 6.1 °C | 18 °C | 95 mm |
| November | 0.3 °C | 9.7 °C | 72.14 mm |
| December | -5 °C | 3 °C | 56.9 mm |
| Annual | 5 °C | 15.6 °C | 1028.21 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 |