Gustnadoes are vortices that form along - usually rapidly-moving - gust fronts. Those vortices may or may not extend to the base of the cloud and may or may not be visible by condensation of water vapour. When connected to a cloud, gustnadoes can be called tornadoes. However, often they are not. It is thought that gustnadoes form as a result of shear-instabilities along the gust front of a storm system.
Tornadoes are favoured by... low LFC heights and high values of CAPE released below 3 km pre-existing vertical vorticity LCL heights below 1500 m, preferably below 1000 m (strong) mesocyclonic tornadoes are favoured by... strong low-level (0-1 km) storm-relative helicity strong low-level (0-1 km) wind shear of around 10 m/s or higher Non-mesocyclonic tornadoes are favoured by a pre-existing wind shift lineweak low-level (0-1 km) shear of 5 m/s or lowerpre-existing low-level vertical vorticity, for example along a convergence line or sea- or land-breeze front |