Tornadoes are extremely unlikely when the atmosphere contains no spin.

Tornadoes occur when strong thunderstorms start to rotate. The rotation comes from wind shear. Changing wind speed and direction in both the horizontal and vertical planes can cause an overturning motion in the atmosphere. If the air could be dyed, one would see huge rotating cylinders along the horizontal plane. When this spin is entrained into a developing thunderstorm, the axis of the rotation is lifted and becomes vertical. In turn, the storm cloud itself starts to rotate. When this spin tightens in one portion of the storm, a tornado often drops from the base of the cloud.

The current state of the atmosphere over the Southeastern states does exhibit enough wind shear for tornadoes to form. At the surface, the air is coming in from the south and southeast, while winds aloft are from the southwest. The rotation being created by the wind shear is being randomly channeled into developing storm clouds, thus the potential for tornadoes exists. The highest threat period was through the first half of Thursday night.

By the way, if you are a doppler radar hawk, understand that tornadoes are more likely to be spawned from a lone thunderstorm rather than those that make up a solid line.

Story by Expert Senior Meteorologist John Kocet.