If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Dearborn: The hottest months are usually July and August, with an average temperature of 21°C, while the coldest months are January and February, with an average of -1°C. The snowiest months in Dearborn are January, February, November and March, with each month seeing an average of 15 cm of snowfall.