The supercell is the most severe of all thunderstorms. It can form out of a generic multicell storm, if there is enough directional windshear in the atmosphere to slant the updraft and separate the cool downdraft from the updraft. The main updraft can strengthen and start rotating due to the air vorticity and mesoscale inflow/outflow pattern; rotation in a storm is an indicator for supercellular behaviour. Supercells create their own small low-pressure systems with fronts (usually in the form of a flanking line and gustfront). They can last several hours and spawn tornadoes, wall clouds and drop very large hail (in rare cases up to 10 cm or 4").
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