Jewett, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.8 °C (low) to 18.2 °C (high). Annual precipitation averages 1140.5 Millimeters. Jewett is located in USDA Plant Hardiness Zone 6b. 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 | -6 °C | 2.9 °C | 78.74 mm |
| February | -4.4 °C | 5.6 °C | 63.25 mm |
| March | 0.7 °C | 11.8 °C | 85.09 mm |
| April | 6.4 °C | 19.2 °C | 123.95 mm |
| May | 12.5 °C | 24.3 °C | 125.22 mm |
| June | 17.3 °C | 28.9 °C | 132.33 mm |
| July | 18.9 °C | 30.7 °C | 108.46 mm |
| August | 17.8 °C | 30.1 °C | 79.5 mm |
| September | 13.3 °C | 27.2 °C | 80.26 mm |
| October | 7.2 °C | 20.5 °C | 91.95 mm |
| November | 1.4 °C | 12 °C | 96.01 mm |
| December | -3.2 °C | 5.4 °C | 75.69 mm |
| Annual | 6.8 °C | 18.2 °C | 1140.45 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |