boots for Christmas trip to Germany and Austria?

Definitely don't hope for good weather (yes, it could happen but you'd want something warm for sure). I'd wear them and all my heaviest and bulkiest items on the plane. Perhaps put on a pair of slipper socks and stick the boots in a plastic bag once you're on the plane and put them back on before landing. I'd make sure they're comfortable enough for all-day wear and pack a comfortable second pair of shoes.

Absolutely necessary? If you plan to walk through a lot of deep unshoveled snow. You can probably count on some snow in Garmisch and maybe Füssen. If you absolutely want to prevent any chance of snow getting in your shoes, OK, go with the snow boots. But you can get by without them. Don't bother with hiking boots, your hiking options are limited around Christmas. If you're going to be mostly walking around in towns, a warm pair of wool socks would probably serve you better than boots.

I would suggest that, rather than packing either hiking boots or snow boots, you consider a pair of ankle boots that are designed for city wear (flats, without heels). They are lighter and more comfortable than either hiking or snow boots, look nice in any situation, and would keep your feet warm and dry. I have a pair of black leather ankle boots by Ecco that are fleeced-lined and have sturdy, gripping soles, but they look quite nice for city wear. The tops look like any nice leather shoes, except they come up higher. They are comfortable to wear anywhere. Many other brands make styles such as this as well.

Thank you for your thoughts. Warmth is one issue, the other is slipping on fresh snow/ice (not so much deep snow). So I was thinking that the treads on snow or hiking boots would keep me from falling and keep my feet warm. The ankle boots are one idea, if I can find one with good treads. However, for my teenage aon, the hiking boots may be the better option. I guess I'm still mulling this over.

When very cold many hiking boots treads will freeze and get slippery. I have also found that the sole will harden and get stiff and uncomfortable. Bottom line - if its snowy and icy and cold, I don't wear my hiking boots.... FWIW (you may have boots which stay supple and all above is wrong)

I was in Germany in '09 when they had those record breaking temps (-16!) and all of the airports were shut down. I wore a pair of chukkas that were waterproof and about ankle height, uninsulated. I wore some Smartwool socks in them and never had a problem. I wouldn't bother with big, bulky boots on your trip. If your feet get cold, stop into a cafe and get come gluwein or something while your feet warm up. I was in all of the cities that you mention (except Trier) and the sidewalks were all maintained to the point where higher boots weren't necessary. And we got LOTS of snow while there.

Hiking boots may be too heavy for normal walking in the city. I took some water proof light weight ankle boots for a trip to that area during Christmas, with good wool socks. I also took a pair of Yak Trax in the event of snow. You can slip these on over the bottom of your boots - they give you tread/traction on snow and ice and are lightweight - sort of like chains for tires but they are for shoes. I use them for when it snows here or when I go to snowy areas and they are great!

Knee-high boots are still the rage here now. I have more casual ones by Clarks that are super comfortable for all-day wear. Worn with the smart-wool socks, very warm, too. The sidewalks are usually shoveled quickly, so deep snow in town usually isn't a problem. Whatever you would wear in December in Bellevue or downtown Seattle is what you should wear here.

I love my LLBean knee high hiking boots. They are not that heavy for packing, but I like the suggestion of wearing them on the plane. When I do this, I don't lace it up all the way, and then they are incredibly easy to slip on when on the plane and stay on my feet with no problems. The suggestion of taking those hospital-style socks on the plane to wear is a good one as well. They are disposable, so I take two and toss them when all done. Just put your boots in the overhead bin. Or take a pair a lightweight slip-ons/sandals. I would take boots. Surprisingly, wool socks are not recommended in cold and wet weather. Buy a couple of pair of skiing socks. They will keep your feet much warmer.