Brillion, Wisconsin has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.3 °F (low) to 54.6 °F (high). Annual precipitation averages 32.2 Inches. Brillion is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 10.3 °F | 25.4 °F | 1.38 in. |
| February | 12.2 °F | 28.8 °F | 1.08 in. |
| March | 22.5 °F | 40.2 °F | 1.7 in. |
| April | 34.1 °F | 53.7 °F | 3.01 in. |
| May | 45.8 °F | 66.6 °F | 3.68 in. |
| June | 56.2 °F | 76.2 °F | 4.59 in. |
| July | 60.3 °F | 80.7 °F | 3.77 in. |
| August | 58.5 °F | 78.9 °F | 3.4 in. |
| September | 50.7 °F | 72.1 °F | 3.16 in. |
| October | 39.2 °F | 58.0 °F | 2.87 in. |
| November | 28.4 °F | 43.9 °F | 1.93 in. |
| December | 17.1 °F | 31.0 °F | 1.58 in. |
| Annual | 36.3 °F | 54.6 °F | 32.15 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |