Other facts from our historical weather data: Which is the warmest month in Cwm-y-glo? July has an average maximum temperature of 19°C (66°F) and is the warmest month of the year. Which is the coldest month in Cwm-y-glo? The coldest month is February with an average maximum temperature of 9°C (48°F). Which is the wettest month in Cwm-y-glo? December tops the wettest month list with 139mm (5.5 in) of rainfall. Which is the driest month in Cwm-y-glo? May is the driest month with 88mm (3.5 in) of precipitation. Which is the sunniest month in Cwm-y-glo? May is the sunniest month with an average of 169 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.