The best wave days start early.  Assembly during false dawn and launch at the moment of sunrise is common.  It will be cold.  If you get hot on the ground during assembly, often your feet will have sweated.  Foot warmth is usually the biggest (body) issue at altitude.  We usually assemble with only light clothing, changing into flight clothing just prior to launch.  Generally, this includes changing socks and using baby powder on the feet to assure they are dry.