Weather will likely play an important role when you plan your trip to McHenry, but bear in mind that cheaper options are usually available when the weather isn't as good. 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 0°C. The snowiest months in McHenry are January, December, February and May, with each month seeing an average of 79 cm of snowfall.