Without a dress code, either long or short dress is ok! Maybe long sleeved and paired with some opaque tights for colder weather. Lots of holiday party dresses out now can also double well as wedding guest outfits. More on reddit.com

It depends on the dress code and venue! I went to a formal wedding in a Colorado that had the ceremony outside in the (snowy!) winter. You can get formal dresses in warmer/heavier fabrics. I wore this velvet dress to get a heavier fabric for warmth ( https://www.kiyonna.com/products/verona-velvet-evening-gown?variant=44967954415921&tw_source=google&tw_adid=&tw_campaign=18136139413&tw_kwdid=&gad_source=1&gad_campaignid=17347378721&gbraid=0AAAAAD-9aijPdOuboNfLScVk8AbfIg4S-&gclid=Cj0KCQjws4fEBhD-ARIsACC3d29NF3-Md2Cm01_YFgTfPgSAu4mWvlM0uBA5eV_zLeg1KmhV_ifg_WUaAm2SEALw_wcB ) Layers can be your friend if you will have to be outside much (or even while transiting). Pashminas and shawls can come in more lux fabrics that can be good lighter-weight layers, or a formal coat/peacoat can be used if you will be outside much. Gloves (can’t go wrong with black formal ones) or tights/hosiery can help too. More on reddit.com

That’s a lovely dress. More on reddit.com

Do you normally wear dresses? I think the expectation isn't usually as high if you're not actually part of the bridal party, so you could probably get away with a nice pant suit or whatever. I'd just be hitting Google for winter wedding outfits or something 😂 If you're travelling from Auckland to Ireland, your very presence will surely buy you some leniency~ I'm not helpful at all. I might put that in my bio More on reddit.com