December in Keflavík is the coldest month of the year. In December, the weather in Keflavík is typically cold. Average daily high temperature in December is about 3 degrees above zero. On average, Keflavík has 24 rainy, 4 sunny, and 3 cloudy days in December. The rains are usually heavy. December as well as January, February, March, and April is considered the most uncomfortable time to visit Keflavík.