The Supercell:King Of All Thunderstorms
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A supercell is an elite type of thunderstorm accompanied by dangerous weather conditions including large hail,damaging winds and,sometimes,tornadoes.
What Sets Them Apart
An ordinary thunderstorm in the middle of summer can produce lightning and a heavy downpour. But within an hour or less,it rains itself out and fizzles. Supercell thunderstorms,however,can last several hours and track hundreds of miles. The key to that longevity is wind shear.
If winds above the ground are much faster and from a different direction than near the ground,that causes the air between to spin slowly around a horizontal axis. You can visualize this by placing a pencil flat between your hands and moving your hands in opposite directions.
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In that environment of high wind shear,a growing thunderstorm's upward current of air,or updraft,tilts that horizontal tube of rotation upright. It also stretches that tube vertically,which makes it spin faster.
That becomes the supercell's "mesocyclone". And this mesocyclone can set up pressure differences within the supercell that maintain the updraft's strength and rotation in a bit of positive feedback.
Another reason wind shear helps maintain these longer-lived supercells is the storm's rain and hail is blown downwind,instead of raining down and choking off the storm's updraft,as with an ordinary thunderstorm. You can see that labeled in the diagram below as the "forward flank downdraft".
Supercell Types
Classic
Classic supercells appear as individual storms,but sometimes can be embedded within a line or cluster of thunderstorms.
Supercells have a distinct appearance on Doppler radar,which often features a so-called hook echo on the southwest flank of the storm. That hook echo appendage extends southward from the thunderstorm's main core,where large hail and heavy rain are typically located. When tornadoes are spawned by supercells,they are near the hook echo on radar.
When viewed in an open area,classic supercells have a "mothership"appearance often photographed in the Plains states.
High-Precipitation (HP)
High-precipitation or HP supercells contain heavier concentrations of rain and hail wrapping into the mesocyclone. The precipitation can sometimes obscure the storm's structure,including wall clouds and tornadoes. Tornadoes obscured by heavy precipitation are typically known as "rain-wrapped."
Low-Precipitation (LP)
As the name implies,an LP supercell is accompanied by lighter precipitation. In some cases,the only precipitation that falls are very large,sporadic hailstones.
This type of smaller supercell is usually found in the Plains or High Plains. It's easy to spot by its distinctive,bell-shaped structure.
Impacts
Tornadoes
According to the National Severe Storms Laboratory (NSSL) as few as 20% of all supercell thunderstorms produce tornadoes. However,supercells are responsible for spawning most tornadoes – violent ones in particular. Research continues today to figure out why some of these rotating thunderstorms are accompanied by tornadoes while others are not.
The best-organized supercells may spawn multiple tornadoes,known as a tornado family. Some of these can stay on the ground for a long time,sometimes up to an hour or so.
One of the most egregious examples of this was the Greensburg,Kansas,EF5 tornado on May 4,2007. That deadly tornado was only one of 22 tornadoes spawned by a single supercell.
Huge Hail
Quite often,especially in the Plains states,the extreme instability helping to fuel supercell thunderstorms can lead to prolific hail.
For example,a supercell in mid-May 2021 in northeast Mexico dumped spiky-looking grapefruit-size hail.
And on Aug,1,2022,a supercell heavily damaged vehicles on a main road between Calgary and Edmonton,Alberta,Canada.
Not Just In The Plains
While supercells are often documented in the Plains,Midwest or South,that doesn't mean they can't happen elsewhere.
They've been witnessed,on occasion,in California's Central Valley in January.
They can even happen in paradise. In March 2012,a supercell dumped hail of a diameter larger than a softball on the island of Oahu,Hawaii.
And they're not just an American phenomenon. They can happen anywhere around the world when conditions align,such as parts of Europe and the Río de la Plata basin of South America.
Chris Dolce has been a senior meteorologist with www.weathernow24.com for over 10 years after beginning his career with Weather Now 24 in the early 2000s.
Jonathan Erdman is a senior meteorologist at www.weathernow24.com and has been covering national and international weather since 1996. Reach out to him on X (formerly Twitter),Threads,Facebook and Bluesky.
