Alton, Indiana has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 7.4 °C (low) to 19.8 °C (high). Annual precipitation averages 1315.2 Millimeters. Alton is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.1 °C | 6.1 °C | 97.03 mm |
| February | -2.6 °C | 8.8 °C | 92.71 mm |
| March | 1.4 °C | 14.2 °C | 122.68 mm |
| April | 6.7 °C | 20.3 °C | 131.83 mm |
| May | 12.2 °C | 25.1 °C | 144.78 mm |
| June | 16.7 °C | 29.3 °C | 124.97 mm |
| July | 18.8 °C | 30.9 °C | 113.28 mm |
| August | 18.2 °C | 30.6 °C | 81.03 mm |
| September | 14.1 °C | 27.6 °C | 98.04 mm |
| October | 7.4 °C | 21.7 °C | 97.79 mm |
| November | 1.9 °C | 14.3 °C | 99.06 mm |
| December | -1.7 °C | 8.2 °C | 112.01 mm |
| Annual | 7.4 °C | 19.8 °C | 1315.21 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |