There are three types of supercell storms that have hit our region these days.
Source: Profimedia
A supercell storm like the one that hit the region yesterday is a thunderstorm characterized by the presence of a mesocyclone: a deep, constantly rotating updraft.
Because of this, these storms are sometimes called rotating thunderstorms. Of the four classifications of thunderstorms (supercell, line, multicell, and single cell), supercells are the least common and have the potential to be the most severe. Supercell storms are often isolated from other thunderstorms and can dominate local weather up to 20 miles away. They last 2-4 hours. They can bring with them some of the most dangerous weather events such as tornadoes.
Why are supercell storms so dangerous?
Supercell storms often bring i a city that can be the size of a grapefruit. Despite their intensity, supercell storms are relatively small compared to most thunderstorms. Supercell storms are usually no larger than 12 miles (19.3 kilometers) in diameter. Because of this, one settlement could be ravaged by wind and hail, while the next could pass untouched.
Rising as high as 10 miles (16.1 km), supercell storms can contain an air volume up to 25 times the size of Mount Everest. The secret to a supercell storm’s power is its isolation. These loners do not share their environment with neighboring storms. This allows them to swallow all the surrounding air as “fuel”. While most thunderstorms form in a line and are characterized by multiple updrafts — or pockets of rising air — supercell storms are different. They have only one updraft. But it is extremely powerful. That’s why supercell storms are small but fierce.
What really sets supercell storms apart is their rotation. The entire storm rotates due to the so-called wind shear, that is, the difference in wind speed or direction between two points in the Earth’s atmosphere.
Types of supercell storms
There are three types of supercells: nlow precipitation (LP), classic and high precipitation (HP). The configuration of severe weather wind shear profiles is critical in diagnosing what types of supercell storms can be expected on a given day. While there are many factors that go into determining a supercell storm, one of the most important factors is an analysis of the winds associated with the storm, especially in the upper levels (or anvil level) of the supercell cloud.
Classic supercell storms often occur in environments where storm-related winds are between 40-60 knots. These types of supercell storms can be called ‘Goldilocks’ supercell storms because they don’t have much precipitation. It is considered a pure form of a supercell storm, which also hit our region, while the other two types are hybrids.
The most classic example is a type of storm called “Hook Echo”, which has counterclockwise winds and looks like a notch on the radar. Where the notch bends is usually a tornado cloud. The strongest tornadoes form under these storms. Depending on the air humidity, a city of different sizes can form. Low precipitation supercell storms contain a small and relatively light precipitation core (rain/hail) that is well separated from the updraft. Updrafts are intense, and LPs are inflow-dominant storms. The updraft tower is usually steeper and the deviant motion to the right less than in other types of supercell storms. They can occur if the upper storm level winds are 60 knots or more. A low-precipitation supercell storm usually forms during the summer season when humidity is low. They are famous around town, often the size of a golf ball, without rain. Tornadoes seen in low-precipitation storms are weaker compared to those with heavy precipitation or classic supercell storms.
How do supercell storms form and why are they so powerful?
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High-precipitation supercell storms have a much heavier precipitation core that can wrap around the mesocyclone. These storms also cause flooding from heavy rain, damaging gusts, and weak tornadoes, although they are known to often produce strong tornadoes. These are particularly dangerous storms, as the mesocyclone is enveloped in rain and can hide the tornado (if present) from view. That’s why they can be the deadliest.
How do tornadoes form?
Tornadoes are one of the most feared weather events on Earth. These fast-forming and mostly short-lived cyclones tend to form from supercell storms. Driven by a long-lasting tower of rising air, these storms can unleash some of the fastest surface winds on Earth.
In the Northern Hemisphere, the turning of a supercell storm usually requires moist southerly winds on land. This stirs up a storm. That storm also needs dry mid-level air. It helps if the dry air comes from the west. Those conditions tend to prevent surface air from rising – until an explosive updraft breaks through this layer.
Finally, the storm needs cold air aloft, coming in from the northwest. Air will rise as long as it is thinner – which usually means warmer – than the air around it. The cold upper atmosphere complements this highly unstable environment: it allows the growing storm to rise unhindered. The rotating base of the storm cloud evolves into what scientists call a mesocyclone.
When all these conditions come together, air can spiral toward the south side of the storm. That air then turns into a vortex. That vortex has a very strong suction power. The moisture in its air condenses quickly to form a cloud. This is due to air pressure: it is lower inside the column of rotating air than outside it. In fact, that’s why the tendrils of clouds that move to form a tornado seem to materialize almost out of thin air.
When the conditions are met, the rotation can spin more tightly and form a narrow tube. This funnel cloud is what can become a tornado. The rotating finger-like protrusion of the funnel often coils like a snake towards the surface. Only when it reaches the ground does it officially become a tornado.
(WORLD/Blic)