December in Alpharetta is the cloudiest month of the year. In December, the weather in Alpharetta is typically warm. Average daily high temperature in December is about 11 degrees above zero. On average, Alpharetta has 10 rainy, 10 partly cloudy, 9 sunny, and 2 cloudy days in December. The rains are usually heavy. December as well as January, February, March, and July is considered the most uncomfortable time to visit Alpharetta.