December in Onna is the windiest month of the year. In December, the weather in Onna is typically warm. Average daily high temperature in December is about 19 degrees above zero. On average, Onna has 18 rainy, 6 sunny, 4 partly cloudy, and 3 cloudy days in December. The rains are usually heavy. December as well as January, February, May, and June is considered the most uncomfortable time to visit Onna.