December in Dumas is the cloudiest and the coldest month of the year. In December, the weather in Dumas is typically cold. Average daily high temperature in December is about 7 degrees above zero. On average, Dumas has 16 sunny, 14 partly cloudy, and 1 rainy day in December. The rains are usually heavy. December as well as January and February is considered the most uncomfortable time to visit Dumas.