Weather can make or break a road trip, so we've gathered some data about year-round temperatures in McHenry to help you plan yours. The hottest months are usually July and August, with an average temperature of 19°C, while the coldest months are January and February, with an average of -9°C. The snowiest months in McHenry are April, March, December and October, with each month seeing an average of 21 cm of snowfall.