Complex sentence: The festival coincides with the annual Winter Music Conference, also held in Miami, however, since expansion to 2 weekends in 2013,the two Ultra weekends are held on the weekends that begin and end WMC.
Split into simpler sentences: The festival coincides with the annual Winter Music Conference, also held in Miami. Since expansion to 2 weekends in 2013, however, the two Ultra weekends are held on the weekends that begin and end WMC.