Gregg Hennum donned his winter gear and climbed atop his snowmobile for a 40-mile ride, with intermittent stops, across a frozen Lake of the Woods in Minnesota's Northwest Angle. It wasn’t the first time; he’s been doing this every year for the past 20 winters. Nor was it a joyride; there was purpose to his venture: Hennum is contracted by Lake of the Wood Drifters, a snowmobile club, to mark the trails and keep it groomed all season. It was Monday, Dec. 15, and in just a couple of weeks guests at his family’s resort on Oak Island — and at other resorts in the vicinity — would take to the trails for their snowmobiling or ice-fishing adventure. Hennum wanted to make sure...