Landspout

A landspout is a type of a weak tornado. they form during the growth stage of convective clouds by the ingestion and tightening of boundary layer vorticity by the cumuliform tower's updraft (http://en.wikipedia.org/wiki/Landspout). Landspouts most often occur in drier areas with high-based storms and considerable low-level instability (http://en.wikipedia.org/wiki/Landspout). They generally are smaller and weaker than supercellular tornadoes (http://en.wikipedia.org/wiki/Landspout).