When you're travelling with pets, keeping track of the weather can help you make the trip more safe and fun for everyone. The hottest months are usually August and July, with an average temperature of 21°C, while the coldest months are January and February, with an average of 0°C. The rainiest months in Onogawa Onsen are July, December, August and June, with each month seeing an average of 238 mm of rainfall.