December in Plano is the cloudiest month of the year. In December, the weather in Plano is typically warm. Average daily high temperature in December is about 12 degrees above zero. On average, Plano has 16 partly cloudy, 11 sunny, and 4 rainy days in December. The rains are usually light. December as well as January, February, July, and August is considered the most uncomfortable time to visit Plano.