December in Hillsborough is the cloudiest month of the year. In December, the weather in Hillsborough is typically cold. Average daily high temperature in December is about 1 degree above zero. On average, Hillsborough has 10 partly cloudy, 7 sunny, 7 cloudy, 4 snowy, and 3 rainy days in December. The snowfalls are usually heavy. December as well as January, February, March, and April is considered the most uncomfortable time to visit Hillsborough.