December in Pittsburg is the cloudiest month of the year. In December, the weather in Pittsburg is typically warm. Average daily high temperature in December is about 12 degrees above zero. On average, Pittsburg has 13 partly cloudy, 9 sunny, 7 rainy, and 2 cloudy days in December. The rains are usually heavy. December as well as January and February is considered the most uncomfortable time to visit Pittsburg.