January in Philadelphia is the coldest month of the year. In January, the weather in Philadelphia is typically warm. Average daily high temperature in January is about 10 degrees above zero. On average, Philadelphia has 12 sunny, 10 partly cloudy, 8 rainy, and 1 cloudy day in January. The rains are usually heavy. January as well as June, July, August, and December is considered the most uncomfortable time to visit Philadelphia.