For average conditions please check:

http://www.met.ie/

Many people are surprised by Ireland's temperate climate. Its location alongside the Gulf Stream ensures that Ireland usually remains comfortable even in the winter months. Average temperatures throughout the year range from about 2°C-19°C (36°F-66°F).

Even in December and January, with the exception of an occasional chilly rainstorm, the weather will sometimes remain fine for exploring over a period of a few days...but only if you don't mind sometimes getting a bit wet.

Ireland is famous for its rains, which are responsible for Ireland's many shades of green. A "soft rain" is one that is of fine drops a bit thicker than fog that nonetheless is often capable of soaking you to the skin after only a few minutes. A "lashing rain" usually means one where the water is coming at you from the side, seemingly horizontally. A "shower" lasts just a few minutes (and sometimes the sun will still be shining throughout). A "bucketing rain" is exactly what it sounds like -- waves of water dumping over your head as from a bucket.

It's generally best to be prepared for at least some rain during any given day. Expect more rain in the west of the country than in the east, due to their higher hills.

An Irish writer once wrote that Ireland got "four seasons in one day": the day might start off with light showers of spring-like rain, mid-day would blossom into a brilliant summer's day, afternoon might bring a sudden dry wind, and evening could settle into a chill that goes through your bones.

Do remember that, in the winter months, sunset usually comes around late afternoon. Add to that the amount of cloud cover on a typical winter day, and you may end up with a very short daylight period in which to see the sights. To make up for this, days during the spring and summer months can be very long: it's not unusual for the sky to still be fairly light at 10:00 pm or later. (Keep an eye on the time if you have dinner reservations!)

www.meteireann.ie is the Irish Government Meteorological Service.  This provides weather forecasts and also statistics - so you can go to the area you are going and look at the statistics for the last few years.  This will give you an idea of the average weather conditions.

Climate of Ireland      This is an easy access to climate, rainfall & sunshine info