January in Filadelfia is the hottest month of the year. In January, the weather in Filadelfia is typically hot. Average daily high temperature in January is about 34 degrees above zero. On average, Filadelfia has 9 rainy, 9 cloudy, 7 partly cloudy, and 6 sunny days in January. The rains are usually heavy. January as well as February and December is considered the most uncomfortable time to visit Filadelfia.