Weather can make or break a road trip, so here's some data about year-round temperatures in Norcross to help you plan yours: The hottest months are usually July and August, with an average temperature of 20°C, while the coldest months are January and February, with an average of -7°C. The snowiest months in Norcross are March, April, January and December, with each month seeing an average of 22 cm of snowfall.