Alton, Indiana has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 45.3 °F (low) to 67.5 °F (high). Annual precipitation averages 51.8 Inches. 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 | 24.7 °F | 43.0 °F | 3.82 in. |
| February | 27.3 °F | 47.8 °F | 3.65 in. |
| March | 34.6 °F | 57.5 °F | 4.83 in. |
| April | 44.1 °F | 68.5 °F | 5.19 in. |
| May | 53.9 °F | 77.1 °F | 5.7 in. |
| June | 62.0 °F | 84.7 °F | 4.92 in. |
| July | 65.9 °F | 87.7 °F | 4.46 in. |
| August | 64.7 °F | 87.0 °F | 3.19 in. |
| September | 57.3 °F | 81.7 °F | 3.86 in. |
| October | 45.3 °F | 71.0 °F | 3.85 in. |
| November | 35.4 °F | 57.7 °F | 3.9 in. |
| December | 28.9 °F | 46.8 °F | 4.41 in. |
| Annual | 45.3 °F | 67.5 °F | 51.78 in. |
| 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 : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |