Merrillville, Indiana has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41 °F (low) to 60.1 °F (high). Annual precipitation averages 40.5 Inches. 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 | 17.3 °F | 32.3 °F | 2.33 in. |
| February | 19.9 °F | 36.2 °F | 2.04 in. |
| March | 28.6 °F | 47.0 °F | 2.37 in. |
| April | 38.6 °F | 60.1 °F | 3.66 in. |
| May | 49.5 °F | 70.8 °F | 4.29 in. |
| June | 59.4 °F | 80.4 °F | 4.69 in. |
| July | 63.9 °F | 83.8 °F | 4.31 in. |
| August | 62.2 °F | 82.3 °F | 4.49 in. |
| September | 54.5 °F | 76.7 °F | 3.48 in. |
| October | 43.0 °F | 64.4 °F | 3.74 in. |
| November | 32.6 °F | 49.5 °F | 2.84 in. |
| December | 23.0 °F | 37.4 °F | 2.24 in. |
| Annual | 41 °F | 60.1 °F | 40.48 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |