A landspout is a tornado that forms as a growing convective updraft stretches pre-existing near-surface vertical vorticity along a boundary, usually without a persistent mesocyclone aloft. NSSL describes it as a tornado with a narrow, rope-like condensation funnel that forms while the parent thunderstorm is still developing and whose rotation originates near ground level.
The formation mechanism
The vertical spin needed for a landspout is already present at low levels along a surface boundary, such as a convergence line, an outflow boundary, or an old front. This spin is often organized into small vortices, sometimes called misocyclones, embedded in the boundary itself.
When a rapidly building cumulus congestus or cumulonimbus updraft develops over one of those misocyclones, it stretches the column vertically. Conservation of angular momentum accelerates the spin, and if the stretching is strong and sustained, the vortex reaches the ground as a tornado. Wakimoto and Wilson's 1989 study of non-supercell tornadoes established this stretching-of-pre-existing-vorticity mechanism as the basis for the class.
How forecasters and spotters read them
Landspouts favor high-based storms in weak-shear, high-instability environments with a strong surface boundary. When a line of towering cumulus develops along a convergence line on a warm summer afternoon in eastern Colorado, the setup is classical.
Radar signatures are usually subtle. Storms may lack a hook echo or mid-level mesocyclone, and the vortex is often too shallow to show a strong velocity couplet aloft. Warning decisions frequently hinge on ground reports and on recognizing the mesoscale setup rather than on radar alone.
Where the label misleads
Landspouts are sometimes described as weak by default. The NWS spotter guide is explicit that they can produce EF-2 or higher damage, so the term describes formation mechanism, not intensity ceiling.
Waterspouts over land, dust-tube tornadoes, and shallow spin-ups on QLCS bookend vortices share some traits with landspouts but are not identical. Treating every non-mesocyclonic tornado as a landspout blurs distinctions that matter for warning and research.
Reporting from the field
A rope-like tornado under a young, high-based cumuliform tower along a boundary in the High Plains is likely a landspout. Report it as a tornado, note the parent cloud type and the presence of a nearby boundary, and describe any visible debris or dust ring at the ground so the local office can act quickly on limited radar signal.