December in Portland is the coldest month of the year. In December, the weather in Portland is typically cold. Average daily high temperature in December is about 6 degrees above zero. On average, Portland has 21 rainy, 5 sunny, 3 partly cloudy, and 2 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 Portland.