(Image: Birmingham, AL April 2011)
What are Supercells?
Supercells are the least common form of thunderstorm yet they are potentially the most violent. Large hail of greater than baseball size, strong damaging winds, and tornadoes can accompany these storms.
To storm chasers, Supercells are the grand catch — they are the bounty which storm chasers most commonly hunt for.
How do supercells form?
A supercell requires several very unique factors coming together in order to see them form. All thunderstorms require three ingredients to form:moisture, instability, and lift.
Supercells, on the other hand, require all three of those plus an additional factor: wind shear.
- Moisture: Supercells require adequate moisture to be present in order to form. On the Plains, the base line for good supercell thunderstorms is usually 50F. For supercells to be tornadic, the base line figures are usually dewpoints of 55F on the High Plains and 60F for the lower plains. These vary setup to setup though.
- Instability and Lift: Unstable air is air that tends to rise when it is lifted. For air to rise, it has to be hotter than the air surrounding it, think about the old saying ‘hot air rises’. That saying is true for the atmosphere as well. Unstable air occurs when the air at the surface is warmed beneath cooler temps aloft. The faster the air tends to rise, the more unstable the atmosphere is.
- Wind Shear: Supercells need to have the updraft rotating, this is accomplished through wind shear or wind which veers (turns westward) and speeds up with height. This wind shear creates horizontal vorticity which is then titled upwards by a strong thunderstorm updraft, creating the deep/rotating updraft supercells require.
http://tornadotitans.com/titan-u/about-supercells/
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