Through laboratory experiments, numerical simulations and theory, we examine

the evolution of plumes as they are influenced by background rotation in a

uniform-density ambient fluid. In all cases the source Rossby number is

sufficiently large that rotation does not directly affect the plume itself at

early times. However, on a time scale on the order of half a rotation period,

the plume deflects from the vertical axis. In some experiments and simulations,

the deflection persists and the flow precesses about the vertical axis. In

other cases, shortly after being deflected, the build up of swirling motion

around the plume causes it to laminarize near the source to form a vortex that

then extends vertically away from the source to form a columnar vortex, which

we refer to as a tornado. For this phenomenon to occur, the plume at the source

must be “lazy”. The dynamics governing plume deflection and

possible laminarization are revealed through analysis of three-dimensional