WAUSAU, Wis (WSAU)   All Marathon County snowmobile trails will open at noon today. Some additional grooming was done yesterday, but trails are still in early-season condition without a lot of packed snow cover. ATVs won't be allowed until February 10. And ATVs are not allowed on the Mountain Bay Trail. For more snowmobiling information, call the county's 24-hour trail information line: 1-888-575-7669.