How Do Tornadoes Form?

The forming of tornadoes is both an amazing and frightening thing, happening in a four-step process that requires the perfect natural conditions.  Below is a closer look at how this powerful force of nature is created. 

Firstly, warm, moist air (usually coming in from the Gulf of Mexico) is lifted by a warm or cold front (cool, dry air from Canada) causing an updraft.  This collision leads to an atmospheric instability; the moisture condenses into clouds and precipitation and forms a thunderstorm.  Most tornadoes form from these thunderstorms.

Image source: youtube.com

Usually, precipitation should counter the updraft.  However, when winds blow precipitation out of the rising air, the updraft strengthens.  This change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere.  Beneath the storm, winds of different speeds called shear form horizontal tubes of rotating air.

When these tubes are ingested into the updraft, they become vertical, and the storm acquires rotation, forming what is called a “supercell.”  Rising air within the updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm.

   ​                                        Image source: ustornadoes.com

The rotating tube is stretched, and the supercell becomes a giant vacuum, sucking air up and away.  As air rushes in to equalize the pressure, the tornado is then completely formed.

WeathermanJim Byrne took up meteorology and journalism at San Jose State University. He served as the chief meteorologist at KCOY CBS 12 and was a freelance weekend-weather reporter for NBC Bay Area. For more weather-related reads, clickhere.