Planning for the weather is a good way to make your trip to Yamakawa Onsen relaxing and enjoyable, especially when you’re splurging. 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 3°C. The rainiest months in Yamakawa Onsen are June, July, August and September, with each month seeing an average of 357 mm of rainfall.