Tornadogenesis is the process by which a tornado forms (feature image). There are many types of tornadoes and these vary in methods of formation.
There are various forms and sub-forms of tornadoes. Although each tornado is unique, most kinds of tornadoes go through a life cycle of formation, maturation, and dissipation.
Classical tornadoes are supercellular tornadoes, which have a recognizable pattern of formation. The cycle begins when a strong thunderstorm develops a rotating mesocyclone a few miles up in the atmosphere. As rainfall in the storm increases, it drags with it an area of quickly descending air known as the rear flank downdraft (RFD). This downdraft accelerates as it approaches the ground, and drags the rotating mesocyclone towards the ground with it. Storm relative helicity (SRH) has been shown to play a role in tornado development and strength. SRH is horizontal vorticity that is parallel to the Inflow of the storm and is tilted upwards when it is taken up by the updraft, thus creating vertical vorticity.
Waterspouts are defined as tornadoes over water. However, while some waterspouts are supercellular (also known as “tornadic waterspouts”), forming in a process similar to that of their land-based counterparts, most are much weaker and caused by different processes of atmospheric dynamics. They normally develop in moisture-laden environments with little vertical wind shear in areas where wind comes together (convergence), such as land breezes, lake effect bands, lines of frictional convergence from nearby landmasses, or surface troughs.
Waterspouts normally develop as their parent clouds are in the process of development. It is theorized that they spin upward as they move up the surface boundary from the horizontal shear near the surface, and then stretch upward to the cloud once the low level shear vortex aligns with a developing cumulus or thunderstorm. Their parent cloud can be as innocuous as a moderate cumulus, or as significant as a supercell.
Landspouts are tornadoes that do not form from supercells and are similar in appearance and structure to fair-weather waterspouts with the exception that they form over land instead of water. They are thought to form in a manner similar to that of weaker waterspouts in that they form during the growth stage of convective clouds by the ingestion and tightening of boundary layer vorticity by the cumuliform tower’s updraft.
Tornadoes sometimes form with mesovortices within squall lines, most often in middle latitudes regions. Mesocyclonic tornadoes may also form with embedded supercells within squall lines.
Mesovortices or mini-swirls within intense tropical cyclones, particularly within eyewalls, may lead to tornadoes. Embedded supercells may produce mesocyclonic tornadoes in the right front quadrant or particularly in certain situations with outer rainbands.
Fire whirls and pyro-tornadogenesis
Most fire or volcanic eruption induced whirlwinds are not tornadic vortices, however, on rare occasion circulations with large wildfires, conflagrations, or ejecta do reach an ambient cloud base, and in extremely rare cases pyrocumulonimbus with tornadic mesocyclones have been observed.
Seven Day Forecast
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