In American English, we call it "Indian summer." Why Indian, I'm not sure, or which Indians, Native Americans or Indian subcontinent. Probably something very politically incorrect. There used to be a phrase "Indian giver" that resulted from a cultural misunderstanding. When given something by a Native American, the white folks were expecting to keep it but the Native Americans didn't view possession in the same way. The Indians saw it more as a sharing. So white folks were offended when the Indians took back their gifts and called those who reneged on giving that pejorative (negative) term. Indian summer is the warm weather that comes in fall after a period of cooler weather. I think of it as a bit of borrowed, soon-to-be returned summer.
It looks quite warm. The square has a very appealing look to it, though that might be different come January.
I hope to have a gorgeous Sunday but it won't be as gorgeous as yours.
How's the weather this month in Paris? I miss Paris everyday, I was just in Paris in July for the third time :) This photo certainly doesn't feel cold and yet fall is approaching :)