Dublin's weather is best described as changeable. Rain showers can come at any time (carry an umbrella even if it looks sunny). February-July is the driest time of year, with an average of about 2 in/5 cm of rain each month. December is usually the wettest, but then again, no one goes to Ireland for the weather.
There are few extremes of hot or cold. July is typically the warmest month, averaging 60 F/15 C; January and February are the coldest, averaging about 40 F/4 C. Snow falls just a few days a year at most.