Late last week I was traveling down to Wilmington, North Carolina when I happened across one of the most astonishing sights I have ever witnessed. A classic, textbook-style supercell thunderstorm...the "king" of all thunderstorms! Supercell thunderstorms are quite rare in this part of the country, but when they do occur they are often accompanied by the most threatening of weather conditions.
A supercell thunderstorm is defined as a thunderstorm containing a deep, continuously rotating updraft...technically known as a mesocyclone. These thunderstorms can last for hours without weakening...and can produce large swaths of damaging wind, hail, and torrential rain. Roughly 30% of all supercell thunderstorms produce tornadoes. The supercell I witnessed late last week did produce an EF0 tornado in New Bern County, North Carolina.
Supercell thunderstorms require a unique set of meteorological conditions that are often non-existent here in the Northeast. They require the perfect balance of instability and shear throughout the lowest 6 kilometers of the atmosphere. The air at the surface must be very warm and moist, which increases buoyancy and allows for the formation of a strong updraft. Wind speeds must increase considerably from the surface to the 6km level, which allows for adequate "tilting" of the updraft. If wind speeds do not increase, precipitation will fall directly into the updraft, which in turns weakens the storm. Finally, the wind direction must gradually veer with height...which allows for the necessary rotation to produce a mesocyclone. These conditions are most often met in the Great Plains States, although they do happen here on occasion.
As destructive as they can be, supercell thunderstorms are among the most beautiful storms that one can witness...from a distance, of course! Cloud tops often extend to heights of 50,000 feet or more...and if the updraft is particularly robust, the "overshooting top" can even extend into the lower portion of the stratosphere! Photographs of supercell thunderstorms are the most striking of all weather photographs, and they are truly a wonder to observe.