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