Alton, Missouri has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 44.8 °F (low) to 68.7 °F (high). Annual precipitation averages 48.5 Inches. Alton is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 23.3 °F | 45.0 °F | 3.04 in. |
| February | 26.4 °F | 49.8 °F | 3.22 in. |
| March | 34.5 °F | 59.5 °F | 4.46 in. |
| April | 44.3 °F | 70.3 °F | 5.4 in. |
| May | 54.0 °F | 77.2 °F | 5.47 in. |
| June | 62.5 °F | 85.2 °F | 3.58 in. |
| July | 66.3 °F | 89.4 °F | 3.99 in. |
| August | 64.9 °F | 89.0 °F | 3.76 in. |
| September | 56.3 °F | 81.8 °F | 3.73 in. |
| October | 44.1 °F | 70.9 °F | 3.71 in. |
| November | 34.4 °F | 58.3 °F | 4.5 in. |
| December | 26.5 °F | 47.5 °F | 3.61 in. |
| Annual | 44.8 °F | 68.7 °F | 48.47 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| 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 | Moderate Drought |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |