Weather will likely play an important role when you plan your trip to Koso-ri, 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 75°F, while the coldest months are January and February with an average of 41°F. The rainiest months in Koso-ri are July, August, September, and June, with each month seeing an average of 9 inches of rainfall.