A Silver Alert has been issued for an 80-year-old Winnebago County man who authorities say may be endangered due to cognitive impairment.The Winnebago County Sheriffs Office is searching for John William Beyer, who was last seen leaving his Oshkosh home around 1 p.m. Tuesday with his sister, Donna Beyer.Authorities say both John and Donna Beyer have dementia and do not have family in the Madison area.Cameras later captured the pair driving near the Wisconsin State Capitol in Madison around 7:55 p.m. Tuesday. Their vehicle was last seen around 9:58 p.m. in Rock County traveling south on Highway 14 near Highway 59.John Beyer is described as: 80 years old 5 feet 9 inches tall 215 pounds Blue eyes Gray balding hairOfficials say the pair is believed to be traveling in a tan 1999 Chevy Malibu with Wisconsin license plate 859VNN.Anyone with information on their whereabouts is asked to contact the Winnebago County Sheriffs Office at 920-236-7300. ...read more read less