Barstow, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.1 °C (low) to 15.7 °C (high). Annual precipitation averages 966.5 Millimeters. Barstow is located in USDA Plant Hardiness Zone 5b. 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 | -9.7 °C | -0.8 °C | 39.12 mm |
| February | -7.7 °C | 1.7 °C | 44.45 mm |
| March | -1.8 °C | 8.8 °C | 64.01 mm |
| April | 4.4 °C | 16.1 °C | 93.73 mm |
| May | 10.9 °C | 22.4 °C | 122.43 mm |
| June | 16.6 °C | 27.7 °C | 122.94 mm |
| July | 18.6 °C | 29.4 °C | 109.22 mm |
| August | 17.4 °C | 28.4 °C | 100.84 mm |
| September | 12.8 °C | 24.9 °C | 88.65 mm |
| October | 6.2 °C | 17.8 °C | 72.14 mm |
| November | -0.4 °C | 9.3 °C | 57.66 mm |
| December | -6.3 °C | 2.2 °C | 51.31 mm |
| Annual | 5.1 °C | 15.7 °C | 966.5 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |