"Winter Blend" in Houston, Pensacola, Miami??
 

Some cities are so far south that they never really experience what many of us would identify as "winter".

Do they still have a transition to a "winter blend", and if so, what is that like? How is the fuel different?

It really depends on your city's average temperature. Living in NM I had to deal with this all winter. The southern cities sometimes wouldn't have winter diesel but Albuquerque north always did.

Interestingly the EPA changes their emissions requirements in areas that use winter fuels.

But to answer your question, as I found out in NM, if a city stays warm enough they never transition to winter fuel. Because of the cold weather additives it's less efficient and dirtier.