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July 4 thunderstorm spawned ‘gustnado’

July 9, 2012
By JOHN PEPIN - Journal Staff Writer ( , The Mining Journal

CHANNING - National Weather Service investigators from the Negaunee Township office have determined that straight line winds and a "gustnado" blew through Dickinson County near Channing on the Fourth of July, toppling trees, power poles and electric lines.

The weather service said the thunderstorms that caused the damage occurred between 6:30 and 6:40 p.m. CDT. A storm damage survey was conducted the following day.

"It was determined that most of the wind damage was caused by straight line winds along the leading edge of a thunderstorm moving into the area. In the yellow area on the map below, most of the damage was confined to sporadic tree damage (uprooted trees and snapped smaller trees) and was consistent with wind speeds in the 60 to 75 mph range," forecasters said in a website report.

Article Photos

Trees fell at the Gust Newberg Park along Sawyer Lake in Dickinson County after straight line winds and a “gustnado” pushed through the Channing area on the Fourth of July. (National Weather Service photo)

The weather service said there were some areas of enhanced damage, where tree damage was more widespread. Forecasters said several of the trees fell on houses and vehicles.

"In addition, several power lines and poles were blown down. Wind speeds in this area were estimated at 75 to 95 mph," the report read.

"While most of the damage was consistent with straight line winds, there was some evidence of some circulation in the damage pattern along the eastern side of the enhanced damage area," the report read. "The signs of circulation in these areas were attributed to swirling winds along and to the east of the apex of the strongest straight line winds. Numerous eye witness accounts indicated several small vortices crossing Sawyer Lake as the strongest wind gusts pushed across the area."

Forecasters said that "since these circulations are on the leading edge of the thunderstorm outflow, they are often referred to as gustnadoes, since they do not form like classic tornadoes."

John Pepin can be reached at 906-228-2500, ext. 206.



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