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Another key ingredient supporting the development of tornadoes is what is known as Wind Shear. Wind shear is basically the change of wind speed or direction over a given distance. For tornadoes to develop, significant speed and directional wind shear with height is very important.
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With the low pressure center located in southwestern Iowa, and winds flowing counterclockwise around it, surface winds at 21Z, or 4:00 PM CDT, were generally from the southeast throughout much of east-central Illinois (shown by the arrows). As analyzed a short time later, mid level winds near 700 mb have veered around and were blowing from the southwest (see panel below).
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This indicates strong directional wind shear over the lower atmosphere, a vital component for tornado development. The vertical wind profile was also evident in the sounding from nearly the same time.
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shear profile |