January in Castlebar is the windiest and the coldest month of the year. In January, the weather in Castlebar is typically cold. Average daily high temperature in January is about 7 degrees above zero. On average, Castlebar has 25 rainy, 3 sunny, and 3 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 Castlebar.