Other facts from our historical weather data: Which is the warmest month in Builth Wells? July has an average maximum temperature of 20°C (68°F) and is the warmest month of the year. Which is the coldest month in Builth Wells? The coldest month is February with an average maximum temperature of 7°C (45°F). Which is the wettest month in Builth Wells? December tops the wettest month list with 112mm (4.4 in) of rainfall. Which is the driest month in Builth Wells? September is the driest month with 81mm (3.2 in) of precipitation. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.