Weather is probably a major factor when you plan your trip to Kamimoku Onsen, 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 January and February, with an average of 0°C. The rainiest months in Kamimoku Onsen are July, September, October and August, with each month seeing an average of 220 mm of rainfall.