Planning for the weather is a good way to make your trip to Wonju relaxing and enjoyable, especially when you’re splurging. 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.