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