Other facts from our historical weather data: When is summer in Philadelphia?The hottest season / summer takes place in June, July, August and September. Which is the warmest month in Philadelphia? July has an average maximum temperature of 31°C (88°F) and is the warmest month of the year. Which is the coldest month in Philadelphia? The coldest month is January with an average maximum temperature of 5°C (41°F). Which is the wettest month in Philadelphia? August tops the wettest month list with 132mm (5.2 in) of rainfall. Which is the driest month in Philadelphia? November is the driest month with 78mm (3.1 in) of precipitation. Which is the sunniest month in Philadelphia? July is the sunniest month with an average of 275 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.