Weather will likely play an important role when you plan your trip to Wonju, 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 71°F, while the coldest months are January and December with an average of 30°F. The rainiest months in Wonju are July, August, September, and June, with each month seeing an average of 9 inches of rainfall.