Weather will likely play an important role when you plan your trip to Wonju, but bear 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 temperature of 21°C, while the coldest months are January and December, with an average of -1°C. The rainiest months in Wonju are July, August, September and June, with each month seeing an average of 218 mm of rainfall.