There’s a fascinating set of pages on the BBC site: The Year So Far. It details averages and means in temperature, rainfall, etc, and how the current year is behaving. Well worth keeping an eye on, I think.
Also from the BBC is a page concerning that most typical of winter weather in these islands: Rain, Drizzle & Fog.
Finally, since I read it with great pleasure a few years ago, I thought I’d provide a link to Eddie Graham’s A Dublin Weather Diary. It’s probably of interest to meteorology geeks more than anyone else, but it details things like the usual dates of the first air frost, the coldest days of the year, and other hard to find information. It was published in 2000, so it probably won’t be completely accurate for the warmer, wetter weather we’ve had since, but it provides a good context.