I apologize in advance, I am sure that this has already been covered, but which European destinations are seasonal?
I am guessing the year-round are
PHL: FRA, CDG, MUC, LGW, MAN, FCO, AMS, BCN, MAD
CLT: FRA, LGW

But what about ATH, LIS, VCE, MIL, ZRH, BRU, VCE, SNN, DUB, STO? Do they all start on the same date, or when does the seasonal schedule go into effect?