July in Letterkenny is the rainiest, the cloudiest, and the warmest month of the year. In July, the weather in Letterkenny is typically warm. Average daily high temperature in July is about 15 degrees above zero. On average, Letterkenny has 30 rainy and 1 sunny day in July. The rains are usually heavy. July as well as January, February, March, and April is considered the most uncomfortable time to visit Letterkenny.