ALGONQUIN – The fog that covered McHenry County on Wednesday isn't going away Thursday, according to the National Weather Service. A dense fog advisory was in effect until 10 p.m. Wednesday, according to the National Weather Service, and more fog is expected Thursday. Thursday also could see light sleet and snow in the afternoon and evening, according to the service. McHenry and surrounding counties experienced less than a quarter-mile of visibility in some areas Wednesday night because of the fog, according to the service.