January in Sunbury is the sunniest and the warmest month of the year. In January, the weather in Sunbury is typically warm. Average daily high temperature in January is about 24 degrees above zero. On average, Sunbury has 17 sunny, 11 partly cloudy, and 3 rainy days in January. The rains are usually light. January as well as December is considered the most comfortable time to visit Sunbury.