December in Houston is the rainiest and the cloudiest month of the year. In December, the weather in Houston is typically warm. Average daily high temperature in December is about 16 degrees above zero. On average, Houston has 15 rainy, 8 sunny, 5 partly cloudy, and 3 cloudy days in December. The rains are usually heavy. December as well as July, August, and September is considered the most uncomfortable time to visit Houston.