How do tornadoes form?
Exactly how tornadoes form is still not completely known. But after many years of study, meteorologists, scientists who study weather, do know some things for sure. Tornadoes can form as part of several different types of storms but they are produced inside powerful thunderstorms more than any other. Tornadoes form where warm, moist air and cold, dry air meet and begin to create updrafts that develop into massive rotating cumulonimbus clouds or supercells. Sometimes a spinning column of air called a vortex forms within these clouds. When this vortex becomes visible as a funnel cloud and reaches the ground, a tornado is created. Not all tornadoes form as part of a thunderstorms. Meteorologists have discovered that sometimes a horizontal layer of air can be set spinning. This happens when it gets caught between two other layers of air that are moving in opposite directions. This would be similar to rolling a pencil between your hands. With the help of updrafts and gravity this column can
The classic answer — “warm moist Gulf air meets cold Canadian air and dry air from the Rockies” — is a gross oversimplification. Many thunderstorms form under those conditions (near warm fronts, cold fronts and drylines respectively), which never even come close to producing tornadoes. Even when the large-scale environment is extremely favorable for tornadic thunderstorms, as in an SPC “High Risk” outlook, not every thunderstorm spawns a tornado. The truth is that we don’t fully understand. The most destructive and deadly tornadoes occur from supercells — which are rotating thunderstorms with a well-defined radar circulation called a mesocyclone. [Supercells can also produce damaging hail, severe non-tornadic winds, unusually frequent lightning, and flash floods.] Tornado formation is believed to be dictated mainly by things which happen on the storm scale, in and around the mesocyclone. Recent theories and results from the VORTEX program suggest that once a mesocyclone is underway,
The truth is that scientists don’t fully understand how tornadoes form. Typically, tornadoes develop several thousand feet above the earth’s surface inside of a severe rotating thunderstorm. This type of storm is called a supercell thunderstorm. The spinning of these supercell thunderstorms is visible via Doppler radar.
This is far from being completely understood. See my essays on tornadoes: (1) thoughts after VORTEX and (2) defining a tornado. Basically, we currently believe many tornadoes come from supercell storms but some tornadoes are produced by non-supercell storms. A supercell is a rotating storm, but not all tornadoes come from supercells and not all supercells produce tornadoes. Trying to understand more about tornadoes was a major purpose of the VORTEX project. Tornadoes develop from weaker vortices that “spin up” into tornadoes. Under the right conditions, the initial weak vortex undergoes a process called “stretching” … not unlike the way an ice skater spins up by pulling in his/her arms … in physical terms, this is known as conservation of angular momentum. Once it begins, the development of a tornado can proceed very quickly … in a matter of a few minutes. The weaker vortices that sometimes become tornadoes apparently can form in a number of different ways, so not all tornadoes h
