Other facts from our historical weather data: When is summer in Riverton?The hottest season / summer takes place in June, July, August and September. Which is the warmest month in Riverton? July has an average maximum temperature of 32°C (90°F) and is the warmest month of the year. Which is the coldest month in Riverton? The coldest month is January with an average maximum temperature of -1°C (30°F). Which is the wettest month in Riverton? May tops the wettest month list with 60mm (2.4 in) of rainfall. Which is the driest month in Riverton? January is the driest month with 6mm (0.2 in) of precipitation. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.