At a Glance Three tornadoes and damaging straight-line winds struck Sioux Falls, South Dakota, Tuesday night.Southern sections of the city have been hardest hit.More than three dozen buildings were damaged.Most of the city's warning sirens didn't sound. As tornadoes and straight-line winds blew off roofs and destroyed buildings Tuesday night in Sioux Falls, South Dakota, most of the city's warning sirens failed to sound. Sioux Falls Mayor Paul TenHaken said Wednesday that the problem was caused when an employee in...