Lake Petersburg, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.7 °C (low) to 17.1 °C (high). Annual precipitation averages 979.9 Millimeters. Lake Petersburg is located in USDA Plant Hardiness Zone 6a. 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 | -7.8 °C | 1.6 °C | 54.36 mm |
| February | -5.9 °C | 4.2 °C | 48.01 mm |
| March | -0.8 °C | 10.8 °C | 65.53 mm |
| April | 5.1 °C | 17.8 °C | 100.33 mm |
| May | 11.6 °C | 23.3 °C | 112.01 mm |
| June | 16.7 °C | 27.9 °C | 112.78 mm |
| July | 18.4 °C | 29.7 °C | 96.77 mm |
| August | 17.2 °C | 28.9 °C | 93.47 mm |
| September | 12.6 °C | 26.1 °C | 83.82 mm |
| October | 6.1 °C | 19.1 °C | 81.79 mm |
| November | 0.2 °C | 11.1 °C | 75.95 mm |
| December | -4.8 °C | 4.4 °C | 55.12 mm |
| Annual | 5.7 °C | 17.1 °C | 979.94 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |