Factoring in the environment

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However, there is more to issuing tornado warnings than simply examining the magnitude of rotation on doppler radar. The favorability of the environment for tornadoes must also be considered. One way to estimate how favorable the environment is for tornadoes is to examine parameters related to low-level instability and shear. Large values of low-level instability and shear are both favorable for tornadogenesis. The nomogram shown on this slide is from research by Togstad et al, and indicates that the expected frequency of a significant tornado, given the existence of a supercell, increases as the 0-3 km vorticity generation parameter increases, and as the 0-1 km shear increases. (The 0-3 km vorticity generation parameter is a function of 0-3 km shear and CAPE and is a measure of the potential for the atmosphere to generate low-level vorticity by tilting and stretching vorticity generated by vertical wind shear).

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