January in Belfast is the windiest and the cloudiest month of the year. In January, the weather in Belfast is typically cold. Average daily high temperature in January is about 7 degrees above zero. On average, Belfast has 19 rainy, 7 cloudy, 3 sunny, and 2 partly cloudy days in January. The rains are usually heavy. January as well as February, March, April, and May is considered the most uncomfortable time to visit Belfast.