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A landspout tornado (or more simply, a landspout) formed on the lake breeze boundary on Tuesday afternoon August 9th just prior to 4pm CDT. This landspout was observed by Melanie Harnacke, the FAA contract observer on duty at Midway Airport. The tornado was estimated to have begun at 3:48 PM CDT and dissipated at 3:58 PM CDT. This was the first tornado within the city limits of Chicago since a brief F-0 on the campus of Loyola University on September 22, 2006.

Here is the definition of a landspout from the National Severe Storms Laboratory (NOAA NSSL): A landspout is a tornado with a narrow, rope-like condensation funnel that forms while the thunderstorm cloud is still growing and there is no rotating updraft - the spinning motion originates near the ground. In the case of the Chicago landspout, there was no rain shower or thunderstorm, just cumulus clouds along the lake breeze. Therefore, without a rain shower or thunderstorm, there was no way for the NWS Chicago radar to detect any rotation in the area where the landspout occurred.

Additional landspout definitions: 

From NWS GlossaryA tornado that does not arise from organized storm-scale rotation and therefore is not associated with a wall cloud (visually) or a mesocyclone (on radar). Landspouts typically are observed beneath Cbs or towering cumulus clouds (often as no more than a dust whirl), and essentially are the land-based equivalents of waterspouts.

Unlike most tornadoes which form beneath a rotating (supercell) thunderstorm, landspout tornadoes form when an area of preexisting rotation near the ground becomes positioned beneath a rapidly developing thunderstorm cloud. The quickly rising air lifting into the cloud stretches the area of rotation near ground level vertically, resulting in an intensification of the spin and the formation of a landspout tornado. Normally landspout tornadoes don't last very long or get very strong, though they can do minor damage before dissipating.

Comparing the Chicago Landspout to Central Illinois Landspouts on May 28, 2014

Photo taken by Melanie Harnacke, Midway Airport Observer Central Illinois landspouts on May 28, 2014
Chicago landspout information Central IL landspouts on May 28, 2014

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