My family and I took a trip to Great Britain including London, Bath, Edinburgh, Belfast and Dublin 2 years ago. We didn't take a tour, but made our own itinerary (next time I'll take a tour which is why I'm browsing this site). . We left the day after Christmas and came back January 15. Over 3 weeks, we had only 3-4 days of rain. It was pretty cold, though, but we bought down jackets and that worked just fine. I must say, we were told at every place we visited: you just missed some terrible weather. So I suppose travelling to Ireland at that time of the year is something of a gamble. However, I'd be happy to do it again--cold and rain or no. The key is to learn how to dress to stay warm and dry--I noticed the locals do that with no problem. One day the younger people in our family left their umbrellas at home, we had to share and we all got wet. Another day, I left my jacket hood down and totally drenched myself when I put it up not knowing the rains had filled it. One benefit of going in winter is that you get to miss all the crowds that summer brings but it's still close enough to the holidays that it's exciting. And Christmas in Ireland is lovely. Good luck!