Raritan, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5 °C (low) to 16.2 °C (high). Annual precipitation averages 980.7 Millimeters. 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 | -9.3 °C | 0 °C | 42.67 mm |
| February | -7.3 °C | 2.6 °C | 47.5 mm |
| March | -1.7 °C | 9.7 °C | 62.48 mm |
| April | 4.3 °C | 17 °C | 97.28 mm |
| May | 10.9 °C | 22.8 °C | 130.56 mm |
| June | 16.3 °C | 27.8 °C | 122.17 mm |
| July | 18.2 °C | 29.5 °C | 102.11 mm |
| August | 16.9 °C | 28.6 °C | 92.46 mm |
| September | 12.3 °C | 25.5 °C | 94.23 mm |
| October | 5.8 °C | 18.5 °C | 76.2 mm |
| November | -0.7 °C | 9.9 °C | 64.01 mm |
| December | -6.1 °C | 2.9 °C | 49.02 mm |
| Annual | 5 °C | 16.2 °C | 980.69 mm |
| 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 : -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 |