Chicago Just Got Its First Tornado in Almost 10 Years

Jon Erdman
Published: August 10,2016
A tornado touched down in Chicago on Tuesday, but apparently it produced no damage and wasn't even accompanied by a thunderstorm.
The bizarre, dusty funnel, known as a landspout, was visible from Chicago's Midway Airport just before 4 Thursday afternoon for about 10 minutes and was photographed by several commuters in Chicagoland.

According to the National Weather Service, the landspout touched down in about a two-block area on the city's near southwest side, south of Ogden Avenue. No damage was reported.

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NWS Chicago ✔ @NWSChicago

Based on assessment of photos, if there's any damage from landspout #tornado, approximate area is circled. #ilwx

11:51 PM - 9 Aug 2016

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It could be seen from the top of Chicago's tallest skyscraper, the Willis Tower.

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Mike Hamernik ✔ @MikeHamernik

New photos of Tuesday's landspout taken from the Willis Tower. Courtesy David Harpe. #tornado #Chicago

1:09 AM - 10 Aug 2016

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This was the first tornado of any kind in the city limits of Chicago since an F0 tornado downed trees and limbs on the Loyola University campus on Sept. 22, 2006, according to the National Weather Service.
From 1954-April 2016, there have been 54 tornadoes in Cook County, according to NOAA's Storm Events Database.
While a landspout is technically a tornado, it differs from what you may consider a tornado.
Landspouts don't need a parent thunderstorm with a rotating updraft. They form when a developing towering cumulus cloud occurs over any near-surface boundary of converging winds.
(WATCH: What is a Landspout?)
In Chicago's case, it was the lake-breeze boundary separating air cooled by Lake Michigan with easterly winds from hotter air over inland locations with winds blowing from the west or southwest.

Radar loop showing the lake-breeze boundary (seen as north-northwest to south-southeast broken line) contributing to the Chicago landspout tornado on August 9, 2016, from 2:39 p.m. to 4:26 p.m. CDT. The landspout was reported at 3:48 p.m.

The boundary, therefore, features very slowly rotating air. Once the growing cumulus cloud's upward motion passes over the boundary, that slowly rotating air becomes stretched vertically and accelerates into what became the landspout.
They are essentially waterspouts over land.
Most landspouts are fairly weak and short-lived. On occasion, they can do minor damage. They are most common in the High Plains, Colorado in particular.
One recent, photogenic landspout damaged a farm near Peetz, Colorado, in late May.
Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7.