Altamont, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.7 °C (low) to 18 °C (high). Annual precipitation averages 1100.8 Millimeters. Altamont is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.2 °C | 2.8 °C | 73.91 mm |
| February | -4.4 °C | 5.5 °C | 60.96 mm |
| March | 0.6 °C | 11.6 °C | 81.53 mm |
| April | 6.2 °C | 18.5 °C | 119.89 mm |
| May | 12.3 °C | 23.9 °C | 123.7 mm |
| June | 17.3 °C | 28.9 °C | 122.68 mm |
| July | 18.9 °C | 30.7 °C | 106.17 mm |
| August | 17.6 °C | 30.1 °C | 80.26 mm |
| September | 13.1 °C | 26.8 °C | 79.25 mm |
| October | 6.8 °C | 20.1 °C | 87.63 mm |
| November | 1.1 °C | 11.8 °C | 93.73 mm |
| December | -3.4 °C | 5.3 °C | 71.12 mm |
| Annual | 6.7 °C | 18 °C | 1100.83 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |