Alto Pass, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.1 °C (low) to 19.2 °C (high). Annual precipitation averages 1272.8 Millimeters. 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 | -4.1 °C | 5.4 °C | 89.15 mm |
| February | -2.5 °C | 8.3 °C | 80.77 mm |
| March | 2.4 °C | 13.6 °C | 116.33 mm |
| April | 7.9 °C | 19.7 °C | 137.92 mm |
| May | 13.3 °C | 24.4 °C | 144.27 mm |
| June | 17.9 °C | 29.3 °C | 124.21 mm |
| July | 20.1 °C | 30.5 °C | 102.62 mm |
| August | 18.8 °C | 30.3 °C | 82.3 mm |
| September | 14.4 °C | 27.1 °C | 86.36 mm |
| October | 8.3 °C | 21.1 °C | 95.5 mm |
| November | 2.7 °C | 13.6 °C | 115.57 mm |
| December | -2.3 °C | 7.4 °C | 97.79 mm |
| Annual | 8.1 °C | 19.2 °C | 1272.79 mm |
| 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 : -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 |