Other facts from our historical weather data: Which is the warmest month in Sterling? 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 Sterling? The coldest month is January with an average maximum temperature of -4°C (25°F). Which is the wettest month in Sterling? September tops the wettest month list with 127mm (5 in) of rainfall. Which is the driest month in Sterling? March is the driest month with 44mm (1.7 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.