Supercell Thunderstorms

All of us know what lightning is, even those of us who are blind can sense nearby strikes. Considerably fewer of us may understand the natural mechanisms that cause lightning to occur. Those that do may be aware of what a supercell is, but such knowledge is generally limited to meteorologists and the interested laypeople with a fascination for storms.

As such, in an article answering the question “what is supercell lightning?”, it makes sense to start by explaining what a supercell is. Lightning producing storms are commonly referred to as thunderstorms for obvious reasons; the discharge of a bolt of lightning results in superheated air following the discharge pathway. That abrupt overheating of the air causes a rapid gaseous expansion, so rapid that it generates a sonic boom that we call thunder. But thunderstorms are not all the same. There are four varieties of thunderstorm: supercell, single-cell, multi-cell, and squall line. Of these, the supercell storms, as the name suggests, are the largest and most severe.

Supercell thunderstorms are also called mesocyclones. They are severe thunderstorms typified by a strong, ongoing rotating updraft. As this suggests, they are frequently associated with storm regions that produce tornadoes, put this is not always the case. They normally occur separated from other forms of thunderstorm, although they can occasionally be found embedded within a squall line.

Lightning occurs when the disparity between the negative and positive charges in nearby regions of the atmosphere or ground, either horizontal or vertical, overcomes the resistance of the air between them. Lightning can fork or sheet between these regions as an electrical discharge, a flow of the negatively charged electrons, that attempts to equalize the electrical charges of the regions. Sometimes the neighboring fields of electrical charge can be quite complex and the resulting lightning can form glowing three dimensional shapes, most commonly spherical, and therefore called ball lightning. Lightning can occur within clouds, between clouds, between clouds and nearby pockets of ionically charged air, and between clouds and the earth below.

The path of that electrical discharge reaches temperatures of up to 30,000 degrees Kelvin (50,000 degrees Fahrenheit), explosively heating the air. The heated air expands ultrasonically initially, but the generated wave soon decays to a sound wave heard as a series of thunderclaps and rumbles due to interaction with the intervening air and the funneling and echoing caused by the topography (shape) of the intervening land.

Lightning is generated by all four types of thunderstorm. Supercell lightning is simply that produced by the most severe type of thunderstorm, the supercell thunderstorm.