Savanna, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 38.9 °F (low) to 59.1 °F (high). Annual precipitation averages 38.3 Inches. Savanna is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 12.4 °F | 29.2 °F | 1.51 in. |
| February | 16.2 °F | 33.8 °F | 1.71 in. |
| March | 27.1 °F | 46.4 °F | 2.34 in. |
| April | 37.7 °F | 60.1 °F | 3.75 in. |
| May | 49.5 °F | 71.5 °F | 4.5 in. |
| June | 59.4 °F | 80.9 °F | 5.33 in. |
| July | 62.8 °F | 84.2 °F | 4.49 in. |
| August | 60.5 °F | 82.1 °F | 3.95 in. |
| September | 52.0 °F | 75.9 °F | 3.65 in. |
| October | 40.6 °F | 62.9 °F | 2.88 in. |
| November | 29.3 °F | 47.4 °F | 2.29 in. |
| December | 19.0 °F | 34.7 °F | 1.92 in. |
| Annual | 38.9 °F | 59.1 °F | 38.32 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |