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Section 8.2 Types of thunderstorms

NOAA Jetstream:

Subsection 8.2.1 Multi-cell thunderstorms

  • composed of several individual single-cell storms at different stages of development (cumulus, mature, dissipating)

  • moderate wind shear tilts storm, preventing quenching from rainfall into updraft

  • gust fronts may produce additional lifting along the surface and trigger the formation of new cells (the gust front can produce phenomena such as shelf clouds)

  • multicell thunderstorms may grow or join to produce mesoscale convective systems

Subsection 8.2.2 Mesoscale convective systems

Squall Line

  • thunderstorms arranged in a line or band

  • along boundary of unstable air, often ahead of cold front

  • Have life spans of 6 to 12 hours or more

  • Extend over several states simultaneously

  • A shelf cloud is often observed above the gust front

  • Divergence aloft and a broad, low-level inflow of moist air favor development of squall lines

Mesoscale Convective Complex

  • An MCC is a complex of individual storms that covers a large area in an infrared satellite image and lives more than 6 hours

  • may form under ridge of high pressure if unstable air conditions at the surface

  • Often form in late afternoon and evening

  • In satellite images give the appearance of a large circular storm with cold cloud-top temperatures

  • Often form underneath a ridge of high pressure; because upper-level divergence can occur in a ridge

  • Do not require as much vertical shear as squall lines

  • Can be maintained by the low-level jet

Subsection 8.2.3 Supercell thunderstorms

Conditions that favor violent thunderstorms…

  • high vertical wind shear

  • low level (900 mbar) jet of mT air (sometimes called the nocturnal jet)

  • capping inversion caused by movement of cT air at around 700 mbar level; increases LI at the surface

  • updrafts tilt this shearing and can develop into a supercell

Supercell Thunderstorms

  • The supercell thunderstorm is a large single-cell storm, sometimes 32 km or more across, that almost always produces dangerous weather

  • Strong wind gusts, large hail, dangerous lightning and tornadoes

  • Require a very unstable atmosphere

  • Require strong vertical wind shear (in direction and speed)

  • Vertical wind shear causes supercell thunderstorms to rotate around a vertical axis

  • strong westerly flow aloft and southeasterly surface winds; vortex tube can be carried vertical by a strong updraft

  • updraft and downdrafts do not interfere with each other: storm may survive for several hours

Supercell Structure

  • mesocyclone: spinning updraft (5 to 20 km across); downdrafts caused by heavy precipitation

  • Like a miniature extratropical cyclone, 5 to 20 km across; 2-5 mbar pressure drop

  • Narrows and rotates more quickly when it stretched, but too large and too slow in rotation to be a tornado


  • rain evaporates below cloud, leading to rapid cooling; cold, heavy air plunges to surface

  • RFD (rear flank downdraft) is cool and relatively dry