If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Oskaloosa: The hottest months are usually July and August, with an average temperature of 22°C, while the coldest months are January and February, with an average of -2°C. The snowiest months in Oskaloosa are January, November, December and February, with each month seeing an average of 17 cm of snowfall.