The official cause of death for a 27-year-old woman found on the shore of Lake Winnebago is exposure to the cold.  She had been reported missing at about 4:40 p-m Saturday.  The Fond du Lac woman’s name hasn’t been released.  Witnesses say she was last seen walking away from an ice shanty at about 1:30 a-m.  The Fond du Lac County Sheriff’s Office says she apparently fell at the shore line.  Deputies found her body at about 6:30 p-m.  Foul play is not suspected.