Supercell thunderstorms are dangerous, severe storms that can produce destructive hail, thunderstorms, and powerful tornadoes.
They are responsible for nearly all of the most violent tornadoes and largest hailstorms in the United States.
This is what makes them so powerful.
Thunderstorms require moisture, energy (meteorologists call this instability), and some kind of lift to form. Typically, lift is created by cold and warm air masses colliding along a line called a front.
When thunderstorms occur, they come in two main forms: single-cell and multi-cell.
Unicellular thunderstorms occur alone and exist on their own. Consider brief afternoon thunderstorms in the spring and summer. Multicell thunderstorms occur when individual storms develop and then merge into lines or clusters.
Supercell thunderstorms are also single cells, but they last much longer, lasting hours instead of minutes. The “super” in the name refers to its extended lifespan.
Supercells have one main characteristic that allows them to stay active longer than other storms. It is a powerful rotating updraft.
Updrafts are columns of air that rush upward during thunderstorms, providing moist air and the energy they need to grow taller and stronger.
All thunderstorms have updrafts, and it’s this rotation that makes supercells the most dangerous.
Updrafts rotate when there is sufficient shear (change in wind speed and direction with height) in the atmosphere. Rotating draws in more moisture and energy, keeping the updraft strong and stable for longer.
When a supercell thunderstorm occurs, it will almost certainly produce some form of severe weather in the form of hail or damaging wind gusts.
According to the National Weather Service, not all supercell thunderstorms produce tornadoes, and only about 20% to 30% of them actually do so. However, tornadoes from supercells are more likely to be at the top of the EF scale.
Supercells also often have a distinctive appearance on weather radar, especially when they are about to produce tornadoes. This is called a hook echo and only occurs in supercells. Its spiral shape is an easy way to spot the supercell’s powerful rotating updraft.
