Other facts from our historical weather data: Which is the warmest month in Letterkenny? 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 Letterkenny? The coldest month is February with an average maximum temperature of 9°C (48°F). Which is the wettest month in Letterkenny? December tops the wettest month list with 119mm (4.7 in) of rainfall. Which is the driest month in Letterkenny? April is the driest month with 91mm (3.6 in) of precipitation. Which is the sunniest month in Letterkenny? May is the sunniest month with an average of 203 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.