Thank you, everyone. Since I'm at GMT+2, we get a new day earlier than most of you other (it is only 15 minutes to Monday, for example).
I spent my birthday by swapping tyres from winter to summer season. I noticed that on my Nokian tyres that I use in the summer time, it says "North America All Season" or something like that. I know that North America is a very large continent, ranging from southern states such as California, New Mexico and Florida up to Washington, Michigan and not to mention all of Canada that follows in the north.
It makes me wonder if it is the legislation that makes these tyres valid in (most part of) North America, but only good for seven months per year in Sweden. As late as the other day I read about a woman who had travelled to visit her family in Michigan, and they had -10 C and snow. Legislation or not, I would not have switched to summer tyres if we right now had that weather...