Saturday’s Storm Declared a Microburst

The National Weather Service is calling the storm that hit southwest Cook County and northwestern Indiana a microburst—a meteorological phenomenon that is difficult to predict.

Mircobursts, such as the one that late Saturday afternoon, can pack wind speeds of up to 160 miles per hour. Often mistaken for tornadoes, microbursts form with sudden ferocity and by definition strike areas of less than 4 kilometers (2.4 miles). There are no telltale cloud formations to indicate their presence, such as a funnel cloud.

Microbursts are caused by a strong downdraft from a thunderstorm. When warm air rises to the thunderstorm, tower precipitation forms. The force of the storm is caused by cool air sinking rapidly. When it strikes the ground, the cool air has nowhere to go but out.

“When you take a garden hose and squirt it on the sidewalk, water goes everywhere,” said Jim Allsop, warning coordination meteorologist for the National Weather Service in Romeoville. “That’s what the cool air of a microburst does.”

Weather spotters clocked the winds from Saturday’s storm at 71 mph, moving in a northeast to southeast direction. The storm and knocked out power to 5,000 businesses and households.

Here are some of the reports of damage from Saturday’s storm filed at the Oak Lawn Police Department:

• A gazebo was airlifted by winds from a yard on the 4000 block of West 107th St. and dropped on a Ford Explorer parked in a driveway next door.
• The branch of a tree on the public parkway fell on a car parked on the 10700 block of South Kenneth Avenue, denting the car’s roof.
• A dead branch from a tree on the public parkway fell on a car on the 9000 block of South 49th Avenue.