© sageandspry/IG
A tree is downed during a high wind event in Marquette, Michigan, on Oct. 24, 2017
A tree is downed during a high wind event in Marquette, Michigan, on Oct. 24, 2017
The low-pressure system intensified from a weak area of low pressure over the Ohio Valley Monday morning to an intense low centered near Sault Ste. Marie, Michigan, early Tuesday morning.
The rate of intensification - a 27 millibar drop in the surface low in 24 hours - satisfied the criterion for atmospheric bombogenesis, or a rapidly strengthening low pressure system.
Winds near the Lake Superior shoreline gusted to over 60 mph Tuesday morning and downed trees and powerlines in over two dozen locations in Alger, Marquette and Schoolcraft counties.
Wind instruments about 115 feet above the lake surface at Stannard Rock Lighthouse, about 40 miles north-northeast of Marquette, Michigan, measured a wind gust of 77 mph Tuesday morning.
Wind gusts to just over 50 mph were also clocked in parts of Duluth, Minnesota.
The National Weather Service office just outside of Marquette warned of "giant waves" Tuesday, possibly up to 25 feet offshore, leading to significant lakeshore flooding and beach erosion.
The NWS office also pointed out in a forecast discussion that lake levels were already running about 10 inches above the October long-term average, which would only worsen the flooding and erosion.
This type of event can happen any time of year, but is most common from October through March, when a powerful, intensifying jet stream disturbance forces air to rise over a strong near-surface temperature contrast.
Early November - and late October, for that matter - have a long, notorious history of intense Midwest windstorms.
Known locally as the "Witches of November" and mentioned in singer Gordon Lightfoot's iconic "The Wreck of the Edmund Fitzgerald" about the 1975 storm responsible for sinking the huge iron-ore ship in Lake Superior, these Great Lakes storms don't always produce much snow, but their fierce winds are a signature feature.
Another such storm in 1998 was actually stronger than the 1975 Edmund Fitzgerald storm, and produced wind gusts over 70 mph in some areas of the Great Lakes.
