Other facts from our historical weather data: When is summer in Carbondale?The hottest season / summer takes place in June, July, August and September. Which is the warmest month in Carbondale? July has an average maximum temperature of 30°C (86°F) and is the warmest month of the year. Which is the coldest month in Carbondale? The coldest month is January with an average maximum temperature of 2°C (36°F). Which is the wettest month in Carbondale? September tops the wettest month list with 43mm (1.7 in) of rainfall. Which is the driest month in Carbondale? June is the driest month with 16mm (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.