Atmosphere Academy: How tornadoes form
We all know what they look like, and we know what they are capable of doing, but do you know how tornadoes form?
There are 4 main ingredients you need for tornadoes to form: moisture, instability, lift, and wind shear. Moisture and instability are fairly obvious, but lift and wind shear are a little more mysterious.
Wind shear is the name given to a change in wind speed and direction over a short distance in the atmosphere. This wind shear can create a rolling pattern in the air flow. As a thunderstorm develops, upward moving winds known as updrafts may lift the rolling column of air and guide it towards the top of the cloud. The now rotating updraft is called a mesocyclone. The parent thunderstorm is called a supercell.
Supercell thunderstorms are the most common source of violent tornadoes. As precipitation develops, rain-cooled air is forced toward the surface, creating what is called the rear flank downdraft or RFD. This downdraft can guide a rotating column of air toward the surface, and tornado formation becomes very likely.
Of course, it’s easy to explain tornado formation with pictures and graphics, but seeing these different features in real-life is difficult. Rain and haze can obscure thunderstorm structure from view, which is why radar is so vital to meteorologists. And even then, there are no certainties.
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