Raritan, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.9 °F (low) to 61.3 °F (high). Annual precipitation averages 38.6 Inches. Raritan 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. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.2 °F | 32.0 °F | 1.68 in. |
| February | 18.8 °F | 36.7 °F | 1.87 in. |
| March | 29.0 °F | 49.5 °F | 2.46 in. |
| April | 39.8 °F | 62.6 °F | 3.83 in. |
| May | 51.7 °F | 73.1 °F | 5.14 in. |
| June | 61.4 °F | 82.1 °F | 4.81 in. |
| July | 64.7 °F | 85.1 °F | 4.02 in. |
| August | 62.4 °F | 83.5 °F | 3.64 in. |
| September | 54.1 °F | 77.9 °F | 3.71 in. |
| October | 42.4 °F | 65.3 °F | 3.0 in. |
| November | 30.8 °F | 49.9 °F | 2.52 in. |
| December | 21.0 °F | 37.3 °F | 1.93 in. |
| Annual | 40.9 °F | 61.3 °F | 38.61 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| 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 | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |