AccuWeather’s Heather Buchman explains the conditions needed for tornado production. It’s wind shear:
In order to get tornadoes to form, you first need thunderstorms to develop. And in order to get thunderstorms to develop, you need three ingredients: moisture, upward motion in the atmosphere (or instability) and a trigger.
All three of these ingredients came together across the lower Midwest Saturday.
The actual storm system and its associated warm front served as the trigger for the severe thunderstorms Saturday afternoon, while warm, humid air flowing northward from the Gulf of Mexico provided the moisture or “fuel.”
A combination of these features in conjunction with support from the jet stream also helped create an unstable environment conducive to thunderstorm development.
What made the thunderstorms become severe and spawn tornadoes was the presence of sufficient wind shear, or a varying of wind speed and direction with altitude.
The AccuWeather chart I received in e-mail says 48 tornadoes were reported Saturday night/Sunday morning. And Tuesday? Well, it might happen all over again to some degree.