Other facts from our historical weather data: Which is the warmest month in Glennallen? 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 Glennallen? The coldest month is January with an average maximum temperature of -14°C (7°F). Which is the wettest month in Glennallen? September tops the wettest month list with 69mm (2.7 in) of rainfall. Which is the driest month in Glennallen? April is the driest month with 15mm (0.6 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.