Other facts from our historical weather data: Which is the warmest month in Hartland? August has an average maximum temperature of 19°C (66°F) and is the warmest month of the year. Which is the coldest month in Hartland? The coldest month is February with an average maximum temperature of 10°C (50°F). Which is the wettest month in Hartland? December tops the wettest month list with 146mm (5.7 in) of rainfall. Which is the driest month in Hartland? May is the driest month with 72mm (2.8 in) of precipitation. Which is the sunniest month in Hartland? May is the sunniest month with an average of 197 hours of sunshine. 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.