Ullin, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 8.7 °C (low) to 19.9 °C (high). Annual precipitation averages 1263.9 Millimeters. Ullin is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3.2 °C | 6.1 °C | 95 mm |
| February | -1.4 °C | 9 °C | 90.68 mm |
| March | 2.9 °C | 14.3 °C | 119.63 mm |
| April | 8.4 °C | 20.3 °C | 136.65 mm |
| May | 14.2 °C | 25.2 °C | 134.37 mm |
| June | 18.8 °C | 29.9 °C | 112.78 mm |
| July | 20.7 °C | 31.6 °C | 98.04 mm |
| August | 19.4 °C | 30.8 °C | 74.17 mm |
| September | 14.9 °C | 27.7 °C | 86.61 mm |
| October | 8.4 °C | 21.8 °C | 98.3 mm |
| November | 2.8 °C | 14.2 °C | 112.27 mm |
| December | -1.1 °C | 8.1 °C | 105.41 mm |
| Annual | 8.7 °C | 19.9 °C | 1263.91 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |