Shards of ice encase the St. Joseph, Mich., North Pier Outer Lighthouse on Lake Michigan after a late January storm this year.
The intense buildup of freezing spray requires winds of at least 15 mph, below-freezing air temperature and water temperature lower than 40 degrees Fahrenheit, says Jordan Gerth, a University of Wisconsin-Madison meteorologist and expert on Great Lakes weather phenomena.
“As waves break near the shore, water droplets are blown by the wind and freeze onto subfreezing structures,” Gerth says. To create this icy spectacle, temperatures plunged in about eight hours from 43 to 17 degrees and winds gusted more than 60 mph. The huge waves froze nearly on contact.
[This article originally appeared in print as "Winter Coat."]