Weather is probably a major factor when you plan your trip to Kosaka, 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 20°C, while the coldest months are February and January, with an average of -1°C. The rainiest months in Kosaka are July, August, September and October, with each month seeing an average of 234 mm of rainfall.