Welcome to my forum. Go to my Weather page for all the info you need including temp averages, current weather, links to radar, etc.
Any answer about rain is going to be general info. Over the past 38 years of traveling to Ireland I generally find April/May pretty good. There is always some rain but seems like more sunshine than rainy days. However, this spring April was great and May was a washout. Same for the fall. Sometimes it is good, other times not. No one on earth can predict it! You roll the dice and just go.
To give you an example of recent weather, on our two week trip we had two days of all day rain and the rest was a mix of off and on 5 minute light rain then sunny and some days partly cloudy. Some days it would rain in the early morning and we thought it would be a wash out, but the skies cleared and it was beautiful.
We considered that to be typical Irish weather. You can never predict Irish weather. Just go and enjoy, but have a raincoat ready. It was hard to find a weather forecast on Irish television. They don't seem to be at all concerned with the weather.
Ireland is green because it has a "Temperate" climate. It rains as the clouds raise with the warmth of the land into colder air higher in the atmosphere. The influence of Gulf stream means that Palm trees can be grown in many places. To be honest I have lived here on the high ground for the past 4 years and use my raincoat very rarely. I go out in the car, have a body warmer and Bush hat and the choice of shoes depends on where and what. The Irish dont worry about things they cant change and the weather falls into that category.
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Two rules for Ireland, Take your time & bring a sense of humour