Other facts from our historical weather data: Which is the warmest month in Roisan? July has an average maximum temperature of 17°C (63°F) and is the warmest month of the year. Which is the coldest month in Roisan? The coldest month is January with an average maximum temperature of -5°C (23°F). Which is the wettest month in Roisan? November tops the wettest month list with 132mm (5.2 in) of rainfall. Which is the driest month in Roisan? February is the driest month with 94mm (3.7 in) of precipitation. Which is the sunniest month in Roisan? July is the sunniest month with an average of 275 hours of sunshine. 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.