Weather will likely play an important role when you plan your trip to Onamia, and keep 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 temp of 66°F, while the coldest months are January and February with an average of 18°F. The snowiest months in Onamia are March, April, January, and December, with each month seeing an average of 7 inches of snowfall.