January in Portsmouth is the snowiest and the coldest month of the year. In January, the weather in Portsmouth is typically cold. Average daily high temperature in January is about 5 degrees above zero. On average, Portsmouth has 8 partly cloudy, 7 rainy, 7 sunny, 7 cloudy, and 2 snowy days in January. The rains are usually heavy. January as well as February, March, June, and July is considered the most uncomfortable time to visit Portsmouth.