December in Eureka is the coldest month of the year. In December, the weather in Eureka is typically warm. Average daily high temperature in December is about 11 degrees above zero. On average, Eureka has 14 rainy, 10 sunny, 6 partly cloudy, and 1 cloudy day in December. The rains are usually heavy. December as well as January, February, March, and November is considered the most uncomfortable time to visit Eureka.