This single-celled storm has only one dominant updraft of moist, feeding air and one dominant downdraft of cooled air, rain, and possibly hail. The supercell’s compact cumulonimbus structure makes it easy to observe and keep up with and its tendency to rotate makes it the most likely to produce strong, long-lived tornadoes. Supercells tend to rotate because the updraft lifts horizontally rotating air (a property known as vorticity) into a vertical column so that the axis of rotation is perpendicular to the ground. This rotating updraft of air is called a mesocyclone and is a precursor to the development of a tornado. Supercells typically move from southwest to northeast, but there are exceptions to this caused by abnormal wind direction and when a supercell splits into two separate storms.
Wind shear allows the downdraft of this storm to be blown away from the updraft, which lengthens its lifespan considerably and differentiates it from standard airmass and pulse thunderstorms. The supercell’s rain-free updraft base is easily seen in most cases in the Great Plains of the US, but there are instances when rain can wrap around and obscure it. The visibility of this updraft base is crucial because that is generally where tornadoes form.
There are three classes of supercell thunderstorms:
Low Precipitation (LP)
In a Low Precipitation (LP) supercell, the amount of rain that falls from the downdraft is minimal and the updraft base and other structure of the storm are clearly visible. LP supercells are great for storm chasing because of their visibility.
Classic supercells have a much more balanced look because they appear to have equal areas of rain-free updraft space and rain-filled downdraft space.
High Precipitation (HP).
A High Precipitation supercell is the most difficult category to chase because the core of the rain and possibly hail-filled downdraft can wrap around the rain-free updraft base. This makes any additional development such as a funnel cloud or tornado very difficult to see. Supercells can either be one of the aforementioned types or morph into any or all of them during the different developmental stages of the storm.
Supercells have a few main components that are identifiable on Doppler radar:
Hook Echo: An easily identifiable visual “hook” on radar that indicates where the rising updraft of the supercell meets the rear flank downdraft, or the secondary downdraft of air that channels rain and hail around the north and west side of the storm. The tip of this hook shape is generally where you would find tornadoes.
Inflow Notch: The inner eastern (right) side of the hook echo where warm, moist air is sucked into updraft of the storm.
Forward Flank Downdraft/Anvil: The right side of a supercell that tends to fan out on radar is the spreading anvil cloud that drifts away from the main core of a supercell. This area contains the powerful primary downdraft that produces heavy rain and in some cases very large hail. The storm can taper off on the right side of this feature in a v-shaped fashion, which is called a V-notch.