January in St Austell is the windiest and the coldest month of the year. In January, the weather in St Austell is typically cold. Average daily high temperature in January is about 8 degrees above zero. On average, St Austell has 16 rainy, 8 partly cloudy, 5 cloudy, and 2 sunny 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 St Austell.