I've been asked several times regarding what's best to wear around Ireland...
"It rains a lot, yeah?"
"It's cold so I should have a jacket right?"
Well, yes, to both of those questions. Ireland does us all favor, in fact, by making it relatively easy to decide what to wear and it's pretty consistent throughout the year. The following is a rough guide on what you can expect throughout each season.
Spring:
It's cool out and it's going to rain. You may see a bit of sun as well. Always have a light rain jacket on you but have a heavy one on standby when it does get really cold.
Summer:
It's cool outside but slightly warmer on average then the spring. There may be a week when it gets properly hot outside and you see a lot of sun but you're still better off having that light rain jacket on standby for when it rains.
Autumn:
It's cool outside but definitely colder on average than the summer. Sometimes you need that rain jacket and sometimes you don't. It won't regularly get that cold this time of year but it's more likely it'd be colder on average than warmer so have a heavy jacket on standby. It's nice when the sun comes out but that isn't that often.
Winter:
It's cool outside but will definitely get cold and windy more frequently than the rest of the year. You may see the sun sometimes but it's rare. Always wear a heavy rain jacket because you never know when it's going to rain and there's not much worse than being stuck outside unprepared when the cold wind brings the pissing rain straight to the face.
In general, some days are nice throughout the year but most of the time it doesn't last long. Throughout the year, you can wake up to a beautiful sunrise but be caught in a sudden spurge of rain on your way to work only to have it clear up after you walk wet and shivering into the office. On the other hand, you could wake up to pissing rain and wind only to layer up and overheat on your way to work since the sun broke through during your commute.
If you want to properly plan what to wear throughout the week, you could check the weather forecast but generally that's not a good idea because it will occasionally rain when the sun was predicted and could be abundant sunshine when you were promised rain the next day. Usually it's not the latter though.
The vast majority of the time the weather forecast is similar to this...
So in general, I tell people to play it safe. Bring a jacket and just assume you'll be rained on. You can always take it off when and if the sun comes out. The occasional sun is also fun pub banter too. But just being realistic, most of the time you'll be drinking inside because the weather is shite.
So please, make that Northface jacket part of your regular wardrobe while over in Ireland. You'll thank me later.
One last thing:
This post just assumes you're in sunny Dublin. If you're in Galway or the rest of the west you can ignore everything I've mentioned about the sun.
You won't be seeing any sun out west.
Cheers