Markham, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41.8 °F (low) to 59.7 °F (high). Annual precipitation averages 39.9 Inches. Markham 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. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 17.2 °F | 32.0 °F | 2.21 in. |
| February | 19.9 °F | 35.8 °F | 2.07 in. |
| March | 29.2 °F | 46.7 °F | 2.4 in. |
| April | 39.4 °F | 59.4 °F | 3.91 in. |
| May | 50.3 °F | 70.2 °F | 4.53 in. |
| June | 60.3 °F | 80.1 °F | 4.55 in. |
| July | 65.3 °F | 84.1 °F | 4.43 in. |
| August | 63.4 °F | 82.3 °F | 4.16 in. |
| September | 56.1 °F | 76.1 °F | 3.22 in. |
| October | 43.9 °F | 63.3 °F | 3.45 in. |
| November | 33.1 °F | 49.2 °F | 2.68 in. |
| December | 23.1 °F | 37.2 °F | 2.27 in. |
| Annual | 41.8 °F | 59.7 °F | 39.88 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |