Bartlett, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.1 °C (low) to 15 °C (high). Annual precipitation averages 991.1 Millimeters. Bartlett is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.6 °C | -0.8 °C | 50.8 mm |
| February | -8.1 °C | 1.4 °C | 48.01 mm |
| March | -2.8 °C | 7.9 °C | 57.66 mm |
| April | 2.8 °C | 14.9 °C | 96.52 mm |
| May | 8.9 °C | 21.3 °C | 126.75 mm |
| June | 14.5 °C | 26.8 °C | 116.33 mm |
| July | 17.3 °C | 29.1 °C | 96.01 mm |
| August | 16.4 °C | 27.9 °C | 105.16 mm |
| September | 12 °C | 24.2 °C | 88.65 mm |
| October | 5.3 °C | 16.8 °C | 86.36 mm |
| November | -0.8 °C | 8.8 °C | 64.52 mm |
| December | -6.3 °C | 2.1 °C | 54.36 mm |
| Annual | 4.1 °C | 15 °C | 991.13 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |