> there are songs written about the temp. being 35C because it was that really special heat day

Do you mean "28° in the shade" perhaps, a French song from 1978 by Jean-François Maurice? https://www.youtube.com/watch?v=vpPnr0mCka4

Been a while I heard it, had to look it up. :) I also recalled mid-30s something, guess that was wrong. Or this is another case of the Mandela effect.