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Weather Ingredients

The weather ingredients that came together on the afternoon and evening of April 3, 1974, were unprecedented -- not only because the conditions were so perfect, but also because the perfect conditions covered such a large area for a significant amount of time.

At the surface, an unusually deep low pressure system moved across the Mississippi Valley into the Western Great Lakes. South winds ahead of this deep low helped push a warm front northward into the Ohio Valley and Southern Great Lakes. Meanwhile, a cold front surged eastward from the Plains States, and plowed into the very moist and unstable air in place over Dixie.

Upper level winds also played a large part in the Super Outbreak, as they added and enhanced the energy of the overall system, by bringing drier and colder air aloft and creating a favorable wind shear environment. Once the thunderstorms began to grow in the heat of the afternoon, this wind shear caused the storms to rotate, which later lead to tornado formation. And because the necessary weather ingredients covered such a large area for such a long time, the storms were able to maintain their strength, and maintain their rotation, so that they could spawn multiple tornadoes.

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