Other facts from our historical weather data: When is summer in Greeley?The hottest season / summer takes place in June, July, August and September. Does Greeley have a dry season? Yes, the months of January, February, March and November are very dry. Which is the warmest month in Greeley? July has an average maximum temperature of 33°C (91°F) and is the warmest month of the year. Which is the coldest month in Greeley? The coldest month is December with an average maximum temperature of 4°C (39°F). Which is the wettest month in Greeley? May tops the wettest month list with 75mm (3 in) of rainfall. Which is the driest month in Greeley? January is the driest month with 9mm (0.4 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.