Severe Thunderstorms – Types and Classifications


Thunderstorms may occur singly, in clusters, or in lines. Some of the most severe thunderstorms occur when a single thunderstorm affects one location for an extended time. Thunderstorms typically produce heavy rain for 30 minutes to an hour. Warm, humid conditions are highly favorable for thunderstorm development. About 10 percent of thunderstorms are classified as severe—one that produces hail at least three-quarters of an inch in diameter, has winds of 58 miles per hour or higher, or produces a tornado.[1]

A simple way to classify storms is to base the categories on their actual physical characteristics. There is a continuous spectrum of thunderstorm types:

Single-Cell Thunderstorm[3]

Often called “popcorn” convection, single-cell thunderstorms are small, brief, weak storms that grow and die within an hour or so. They are typically driven by heating on a summer afternoon. Single-cell storms may produce brief heavy rain and lightning.[2]




Multi-cell Thunderstorm[5]

A multi-cell storm is a common, garden-variety thunderstorm in which new updrafts form along the leading edge of rain-cooled air (the gust front). Individual cells usually last 30 to 60 minutes, while the system as a whole may last for many hours. Multicell storms may produce hail, strong winds, brief tornadoes, and/or flooding.[4]



Squall Line[8]

A squall line is a group of storms arranged in a line, often accompanied by “squalls” of high wind and heavy rain. Squall lines tend to pass quickly and are less prone to produce tornadoes than are supercells. They can be hundreds of miles long but are typically only 10 or 20 miles wide.[6]

The primary threat is straight line damaging winds. Although squall lines can produce hail and weak tornadoes.

The squall line is often preceded by a shelf cloud.  A shelf cloud is a triangular shaped cloud mass which marks the leading edge or the updraft/downdraft region of a squall line.

Damaging winds may occur as the leading cloud mass or shelf cloud passes, especially if the storms are bowing outward.

Supercell storms can occasionally be embedded or precede a squall line which increases the potential of severe weather.[7]

Supercell Thunderstorm[10]

A supercell is a long-lived (greater than 1 hour) and highly organized storm feeding off an updraft (a rising current of air) that is tilted and rotating. This rotating updraft - as large as 10 miles in diameter and up to 50,000 feet tall - can be present as much as 20 to 60 minutes before a tornado forms. Scientists call this rotation a mesocyclone when it is detected by Doppler radar. The tornado is a very small extension of this larger rotation. Most large and violent tornadoes come from supercells.[9]


Bow Echo[12]

A “bow echo” is a radar signature of a squall line that “bows out” as winds fall behind the line and circulations develop on either end. A strongly bowed echo may indicate high winds in the middle of the line, where the storms are moving forward most quickly. Brief tornadoes may occur on the leading edge of a bow echo. Often the north side of a bow echo becomes dominant over time, gradually evolving into a comma-shaped storm complex.[11]


Mesoscale Convective System[14]

A Mesoscale Convective System (MCS) is a collection of thunderstorms that act as a system. An MCS can spread across an entire state and last more than 12 hours. On radar one of these monsters might appear as a solid line, a broken line, or a cluster of cells. This all-encompassing term can include any of the following storm types:

  • Mesoscale convective complex (MCC) - A particular type of Mesoscale Convective System (MCS), an MCC is a large, circular, long-lived cluster of showers and thunderstorms identified by satellite. It often emerges out of other storm types during the late-night and early-morning hours. MCCs can cover an entire state.
  • Mesoscale convective vortex (MCV) - As low-pressure center within an MCS that pulls winds into a circling pattern, or vortex. With a core only 30 to 60 miles wide and 1 to 3 miles deep, an MCV is often overlooked in standard weather analyses. But an MCV can take on a life of its own, persisting for up to 12 hours after its parent MCS has dissipated. This orphaned MCV will sometimes then become the seed of the next thunderstorm outbreak. An MCV that moves into tropical waters, such as the Gulf of Mexico, can serve as the nucleus for a tropical storm or hurricane.[13]

A derecho is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to that of tornadoes, the damage typically is directed in one direction along a relatively straight swath. As a result, the term “straight-line wind damage” sometimes is used to describe derecho damage. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.[15]




  1. Missouri Department of Public Safety – Severe Thunderstorms:
  2. NOAA National Severe Storms Laboratory (NSSL):
  3. Image Source: [Accessed November 16, 2013]
  4. NOAA National Severe Storms Laboratory (NSSL):
  5. Image Source: [Accessed January 12, 2013]
  6. NOAA National Severe Storms Laboratory (NSSL):
  7. NOAA – NWS – Springfield, MO:
  8. Image Source: [Accessed January 12, 2013]
  9. NOAA National Severe Storms Laboratory (NSSL):
  10. Image Source: [Accessed January 12, 2013]
  11. NOAA National Severe Storms Laboratory (NSSL):
  12. Image Source: [Accessed January 12, 2013]
  13. NOAA National Severe Storms Laboratory (NSSL):
  14. Image Source: [Accessed January 12, 2013]
  15. NOAA National Severe Storms Laboratory (NSSL):
  16. Image Source: [Accessed January 12, 2013]