the most common setting for a gustnado is along the gust front of a severe thunderstorm (by many definitions, containing wind speeds of at least ), along which horizontal shear of the wind may be large. a particularly common location is along the rear-flank gust front of supercell storms. gustnadoes probably form owing to shear instability associated with the strong horizontal shear; a relative maximum in vertical vorticity must exist in order for shear instability to be present. the bigger question is probably what the dynamical origin(s) of the vertical vorticity is (are), such as the tilting of horizontal vorticity into the vertical or vertical vorticity in the ambient environment that preexists the storm. along the rear-flank gust front of supercell storms, vertical vorticity very likely has its origins in the upward tilting of vorticity that can occur within descending air in the presence of baroclinity.