In December, the weather in Parsippany-Troy Hills is typically cold. Average daily high temperature in December is about 5 degrees above zero. On average, Parsippany-Troy Hills has 10 partly cloudy, 8 cloudy, 7 rainy, and 6 sunny days in December. The rains are usually heavy. December as well as January, February, March, and May is considered the most uncomfortable time to visit Parsippany-Troy Hills.