Thunderstorm
Unique identifier / Notation
MH0003
Synonyms
None identified.
A thunderstorm is defined as one or more sudden electrical discharges, manifested by a flash of light (lightning) and a sharp or rumbling sound (thunder) (WMO, no date).
Primary reference(s)
WMO, no date. . Accessed 5 December 2019.
Additional scientific description
Thunderstorms are associated with cumulonimbus clouds (WMO, 2017) and are most often accompanied by precipitation that, when it reaches the ground, is in the form of a shower of rain, snow, snow pellets, small hail or hail. Thunderstorms can cause tornadoes, strong winds, and flash flooding (Habitat for Humanity, 2021).
Metrics and numeric limits
Example types of thunderstorms (NOAA, no date a,b; Australian Government, no date):
| Single-cell | 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. |
| Multi-cell | A multi-cell storm is a 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. |
| Squall line | 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. |
| Supercell | A supercell is a long-lived (greater than 1 hour) and highly organised storm feeding off an updraft (a rising current of air) that is tilted and rotating. This rotating updraft – as large as 16 kilometres (10 miles) in diameter and up to ~15,000 meters (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. |
| Mesoscale convective system | A mesoscale convective system (MCS) is a collection of thunderstorms that act as a system. An MCS can spread across large areas and last more than 12 hours. On radar one of these might appear as a solid line, a broken line, or a cluster of cells. |
| Mesoscale convective complex | A mesoscale convective complex (MCC) – a particular type of MCS – 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. |
| Mesoscale convective vortex | A mesoscale convective vortex (MCV) is a low-pressure centre 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. |
| Derecho | A derecho (pronounced similar to ‘deh-REY-cho’ in English) 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 400 kilometres (~250 miles) and includes wind gusts of at least 93 km/h (58 mph) or more along most of its length, then the event may be classified as a derecho. |
| Virga | Thunderstorms can be considered dry if they do not produce any rain at the surface. However, for the fire weather community, a ‘dry thunderstorm’ may be used to describe a storm producing very little rainfall, such that it is not effective in checking fire spread after lightning ignition. The second scenario is more common, although there are rare instances when thunderstorms produce no sensible rainfall. In the purest sense, ‘dry’ thunderstorms produce rain just below the cloud base but due to a very dry atmosphere below the cloud base, the rain evaporates at some point between the cloud base and the ground. Meteorologically speaking, this is called a virga. |
Key relevant UN convention / multilateral treaty
Not applicable.
Examples of drivers, outcomes and risk management
As an example of National Alerting Parameters, the United States Weather Service defines a thunderstorm as a severe thunderstorm when it produces hail one inch (2.54 cm) or larger in diameter and/or winds equal or exceed 58 mph (93 kmh) (NOAA, no date c).
References
Australian Government, no date. . Accessed 5 December 2019.
Habitat for Humanity, 2021. . Accessed 23 March 2021.
NOAA, no date a. . Accessed 5 December 2019.
NOAA, no date b. . Accessed 5 December 2019.
NOAA, no date c. . Accessed 5 December 2019.
WMO, 2017. . Accessed 23 March 2021.
Type
Meteorological and Hydrological
Cluster
Coordinating agency or organisation
World Meteorological Organization (WMO)