Marianne

Wear sweater, raincoat and walking shoes on the plane.

Stellar advice from Kathy. I travel mostly in Fall and Winter for a month and fit it all in my 22 inch roll on carry on. It can be done. You just need to learn how to mix and match outfits and then cull. It's all about figuring what you don't need as opposed to what you do need. You'll LOVE Ireland. Have fun!

Silk long underwear - I get mine from Sierra Trading Post. It's light weight and doesn't take up much room, but it can be a lifesaver when it's cold and damp. Oh, and scarves help, too.

I like to use the vacuum bags. I've tried zip-lock type bags in various sizes and 2-3 manufacturers and they've never worked well. The "real" vacuum bags compress the bulky items, including wooly scarves and hats, and socks and undies too.

I wear a poncho instead of a raincoat. It's light, folds up to nearly nothing, and keeps my backpack dry too. A rain jacket will turn a warm fleece into a cozy windbreaker. Thermal underclothes are thin, lightweight and keep you warm.

Typo. My carryon is the 22 inch Eagle Creek Travel Get Away.

I will second Patty's recommendation for silk long undies!!

You can do it! And I second all of the advice already given (although not a big poncho fan). Silk long undies is a good idea; a thin fleece layer with a fleece vest worked under a rain coat worked great for me last week when we were there. Plus, take a good stocking hat that has wind resistance (North Face is what I wore). It'll really help keep you warm without taking much space.

Take a look at the packing video on Rick's YouTube feed done by one of his tour guide females. It is possible!