Weather is probably a major factor when you plan your trip to Shinyamane 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 19°C, while the coldest months are February and January, with an average of 0°C. The rainiest months in Shinyamane Onsen are August, September, October and July, with each month seeing an average of 178 mm of rainfall.