At the end of March I drove across Europe from south of Spain, and had summer tyres on. The weather conditions were good, so I was fairly confident I would be ok without winter tyres, but a lot of European countries have laws requiring then at certain points of the year.

I knew in my destination country you needed winter tyres until April 1st, but I couldn't find anything clear on all the countries in-between. Austria was actually the toughest, my understanding is their laws are you need winter tires if the road conditions dictate you need them. In some cases snow chains can be used, but not on highways. But this was based on reading English forum posts from 10 years ago, so I have no idea if it's still correct. I tried to find something clear from an official authority (probably doesn't help I don't speak German) or an automobile association website, but couldn't.