Other facts from our historical weather data: Which is the warmest month in Thirlmere? July has an average maximum temperature of 19°C (66°F) and is the warmest month of the year. Which is the coldest month in Thirlmere? The coldest month is February with an average maximum temperature of 7°C (45°F). Which is the wettest month in Thirlmere? December tops the wettest month list with 148mm (5.8 in) of rainfall. Which is the driest month in Thirlmere? April is the driest month with 87mm (3.4 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.