December in Federal Way is the coldest month of the year. In December, the weather in Federal Way is typically cold. Average daily high temperature in December is about 7 degrees above zero. On average, Federal Way has 18 rainy, 7 partly cloudy, 3 sunny, and 3 cloudy days in December. The rains are usually heavy. December as well as January, February, March, and April is considered the most uncomfortable time to visit Federal Way.