Hi Coachbuster !
I didn't notice such a difference, these last days in France... Could you tell me what was the day/the hour where there was a -6°C / +17°C recently ?
Anyway, as France is the most extended European country and as it has the most kind of climates in Europe (Spain is a good contender, too), it's fairly frequent to see huge differences between NW-SE (in summer) or NE-SW (in winter). Though -6°C / +17°C is rather extreme... :o
Today, it was not bad as well, with a balmy +22°C in southern Corsica and a chilly 0°C of maximum in Normandy (in some secluded valleys).
Today morning saw -4°C in Caen (Normandy) and +12°C in Toulon (Var Coast).