December in Flower Mound is the cloudiest month of the year. In December, the weather in Flower Mound is typically warm. Average daily high temperature in December is about 12 degrees above zero. On average, Flower Mound has 15 partly cloudy, 12 sunny, and 4 rainy days in December. The rains are usually moderate. December as well as January, July, and August is considered the most uncomfortable time to visit Flower Mound.