Dear Tom,

You often use the term full-fetch winds when referring to wave heights. What exactly do you mean?

Roger G.  Mokena

Dear Roger,

Wave heights are limited by fetch, the distance the wind can blow across the water. Lake Michigan’s largest waves have been measured at 20-23 feet at the south end of the lake, generated by long-duration full-fetch north winds blowing down the entire 300-mile-length of the lake with speeds in excess of 55 mph. Lake Superior boasts the highest waves on the Great Lakes, with heights approaching 30 feet in violent fall storms like the one that sank the Edmund Fitzgerald in November, 1975. On the virtually unlimited fetch and expanse of this planet’s oceans, waves can tower to more than 50 feet, and in extreme conditions, rogue waves can approach 100 feet.