A misocyclone is a small vertical vortex, roughly 40 meters to 4 kilometers wide, that spins up along a low-level convergence boundary. When a growing updraft anchors over one and stretches it vertically, the vortex can intensify into a landspout tornado.
How they form
The parent process is horizontal shearing instability. Along an outflow boundary, a dryline, or a lake- or sea-breeze front, the low-level wind changes sharply across a narrow zone. That horizontal wind shift concentrates vertical vorticity into a thin sheet, and the sheet breaks down into a series of small vortices spaced along the boundary.
These vortices are shallow, often only a few hundred meters deep at first, and they can exist without any parent thunderstorm. Dust whirls, cloud shreds, or small pendant funnels marching along a boundary in bright sunshine are often visible signatures of misocyclones under weak or no updraft above them.
How they become tornadoes
The step from misocyclone to landspout tornado is vertical stretching. As a growing cumulus congestus or young cumulonimbus develops directly above one of these vortices, its updraft pulls the vortex tube upward. Conservation of angular momentum concentrates the rotation into a narrower, faster spin, and if the stretching continues, a landspout tornado reaches the ground.
This pathway is fundamentally different from supercell tornadogenesis. There is no persistent rotating mesocyclone aloft to begin with. The rotation is already at the surface along the boundary, and the storm above simply amplifies what is already there.
How forecasters and spotters read the setup
Radar rarely sees misocyclones directly, because the vortices are usually too small and too shallow for the WSR-88D beam to resolve at typical operational ranges. Operational recognition depends on watching where developing cumulus lines up over a visible boundary and on spotter reports from the field.
Environmental clues favor the process. Steep low-level lapse rates, modest CAPE, weak deep-layer shear, a visible convergence boundary, and rapidly growing cumulus rooted along that boundary all raise the odds that any tornado will be non-mesocyclonic. A gustnado is the outflow-only cousin: spun up by a passing gust front without a sustained stretching updraft above it, and typically weaker and shorter-lived than a true landspout.