January in Allentown is the snowiest and the coldest month of the year. In January, the weather in Allentown is typically cold. Average daily high temperature in January is about 1 degree above zero. On average, Allentown has 13 partly cloudy, 7 sunny, 5 rainy, 4 cloudy, and 2 snowy days in January. The rains are usually moderate. January as well as February, March, and December is considered the most uncomfortable time to visit Allentown.