A supercell thunderstorm is one of the four types of thunderstorms. The others are the single-cell thunderstorm, the multi-cell thunderstorm, and the squall line. Only the derecho type of squall line is rarer. Supercell thunderstorms can sometimes be found embedded inside squall lines.
Lightning from supercell thunderstorms is more frequent than lightning from other types of thunderstorms. A supercell thunderstorm over Belgium on May 25, 2009, produced 30,000 lightning strikes in three hours. One third of those lightning flashes were cloud-to-ground strikes. High precipitation supercell thunderstorms produce the most lightning of all supercell types.
CLOUD-TO-GROUND LIGHTNING
Most cloud-to-ground supercell lightning is streak lightning. This is the most common type of cloud-to-ground lightning in all thunderstorms, so it is also the most familiar. The zigzags often used to draw lightning represent examples of streak lightning.
Ribbon lightning is a type of cloud-to-ground lightning which is found almost entirely in supercell thunderstorms. It is caused when the ionized passageway for the lightning’s return stroke is blown sideways by the wind, so that whenever multiple return strokes occur, each one is slightly to the side of the next. Depending on the number of return strokes and the speed of the wind, the result is somewhere between several parallel lightning bolts and a vertical sheet of lightning. Only supercell clouds always have the high cross winds needed for ribbon lightning to exist.
INTRA-CLOUD LIGHTNING
Most supercell lightning is intra-cloud lightning. Nearly all the lightning produced by low precipitation supercell thunderstorms is intra-cloud lightning. However, the small amount of rain associated with low precipitation supercell thunderstorms means that any lightning that reaches the ground can start fires. It is also possible for all the rain in a supercell to evaporate before hitting the ground, thereby creating a dry thunderstorm. Lightning from these storms is sometimes called dry lightning.
The anvil crawler is a type of intra-cloud forked lightning which originates from within or just beneath the anvil and leaps to another part of the same cloud. It is most commonly seen at the back end of supercell thunderstorms as they are beginning to decay. This is the same part of the supercell thunderstorm that most often forms a tornado.
POSITIVE LIGHTNING
Five percent of all supercell lightning strikes are high energy positively charged lightning. This type of lightning is much more powerful than standard lightning, the stroke lasts nearly ten times as long, and it comes from much higher up. Some of these anvil-to-ground lightning strikes are the dreaded bolts out of the blue. The towering anvil is the only part of the cloud that carries a positive charge, and only supercell thunderstorms have anvils.
All supercell thunderstorms can produce positive lightning, but only low precipitation supercell thunderstorms can produce a bolt out of the blue. The anvil stretches out miles in front of its parent cloud in all supercell thunderstorms. However, heavy precipitation clouds will make most of the surrounding sky cloudy. A low precipitation cloud has very little water vapor, so there is much less visible cloud cover. The anvil itself is too high up to be seen from the ground. If lightning comes from the anvil, it will seem to strike out of a clear blue sky.
Because positive lightning carries up to ten times the charge and volt difference compared to negative lightning, it is much more dangerous. A single positive lightning stroke can overload lightning discharge wicks and cause an airplane to explode. This is thought to be the cause behind the in-flight explosion and subsequent crash of Pan Am Flight 214 in 1963. Positive lightning was only discovered in the last two decades, so most building and vehicle codes have not been updated yet.
