December in Siem Reap is the coldest month of the year. In December, the weather in Siem Reap is typically hot. Average daily high temperature in December is about 28 degrees above zero. On average, Siem Reap has 12 cloudy, 10 partly cloudy, 7 sunny, and 2 rainy days in December. The rains are usually moderate. December as well as January is considered the most comfortable time to visit Siem Reap.