Tornadoes are extremely unlikely when the atmosphere contains no spin.Tornadoes occur when strong thunderstorms start to rotate. The rotation comesfrom wind shear. Changing wind speed and direction in both the horizontal andvertical planes can cause an overturning motion in the atmosphere. If the aircould be dyed, one would see huge rotating cylinders along the horizontalplane. When this spin is entrained into a developing thunderstorm, the axis ofthe rotation is lifted and becomes vertical. In turn, the storm cloud itselfstarts to rotate. When this spin tightens in one portion of the storm, atornado often drops from the base of the cloud.
The current state of the atmosphere over the Southeastern states doesexhibit enough wind shear for tornadoes to form. At the surface, the air iscoming in from the south and southeast, while winds aloft are from thesouthwest. The rotation being created by the wind shear is being randomlychanneled into developing storm clouds, thus the potential for tornadoesexists. The highest threat period was through the first half of Thursdaynight.
By the way, if you are a doppler radar hawk, understand that tornadoes aremore likely to be spawned from a lone thunderstorm rather than those that makeup a solid line.
Story by AccuWeather.com Expert Senior Meteorologist John Kocet.
