Bartlett, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.5 °F (low) to 59.1 °F (high). Annual precipitation averages 39 Inches. 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 | 14.7 °F | 30.6 °F | 2.0 in. |
| February | 17.4 °F | 34.5 °F | 1.89 in. |
| March | 26.9 °F | 46.2 °F | 2.27 in. |
| April | 37.1 °F | 58.9 °F | 3.8 in. |
| May | 48.1 °F | 70.4 °F | 4.99 in. |
| June | 58.1 °F | 80.3 °F | 4.58 in. |
| July | 63.2 °F | 84.3 °F | 3.78 in. |
| August | 61.6 °F | 82.3 °F | 4.14 in. |
| September | 53.6 °F | 75.5 °F | 3.49 in. |
| October | 41.6 °F | 62.3 °F | 3.4 in. |
| November | 30.5 °F | 47.8 °F | 2.54 in. |
| December | 20.7 °F | 35.8 °F | 2.14 in. |
| Annual | 39.5 °F | 59.1 °F | 39.02 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |