Alto Pass, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 46.6 °F (low) to 66.6 °F (high). Annual precipitation averages 50.1 Inches. Alto Pass 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 24.6 °F | 41.8 °F | 3.51 in. |
| February | 27.5 °F | 47.0 °F | 3.18 in. |
| March | 36.3 °F | 56.5 °F | 4.58 in. |
| April | 46.2 °F | 67.5 °F | 5.43 in. |
| May | 56.0 °F | 76.0 °F | 5.68 in. |
| June | 64.3 °F | 84.7 °F | 4.89 in. |
| July | 68.2 °F | 86.9 °F | 4.04 in. |
| August | 65.9 °F | 86.6 °F | 3.24 in. |
| September | 58.0 °F | 80.8 °F | 3.4 in. |
| October | 47.0 °F | 70.0 °F | 3.76 in. |
| November | 36.9 °F | 56.4 °F | 4.55 in. |
| December | 27.9 °F | 45.3 °F | 3.85 in. |
| Annual | 46.6 °F | 66.6 °F | 50.11 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| 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 |