Weather will likely play an important role when you plan your trip to Oswego, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually August and July with an average temp of 67°F, while the coldest months are February and January with an average of 30°F. The snowiest months in Oswego are January, February, March, and December, with each month seeing an average of 14 inches of snowfall.