The three-dimensional flow transition behind a heated cylinder subjected to a horizontal flow (water is used as the working fluid; $Pr\,{\simeq}\,7$) at a Reynolds number $\hbox{\it Re}\,{=}\,85$ and a Richardson number $\hbox{\it Ri}\,{=}\,1.0$, manifests itself in the far wake as escaping mushroom-type structures from the upper vortices. The origin of the escaping mushroom-type structures lies in the generation of streamwise vorticity in the near wake, which is described as a cyclic process. In the presence of a spanwise temperature gradient in the near wake, streamwise vorticity is generated, which results from baroclinic vorticity production. Owing to these streamwise vorticity regions, low-speed flow will move upwards at so-called in-plume positions resulting in high- and low-speed streaks in the upper half of the wake. Next, ‘transverse’ vorticity is generated by the spanwise gradients in the streamwise velocity component, resulting in counter-rotating vortices directly behind the cylinder. These vortices lead to high- and low-temperature regions in the spanwise direction and the process repeats itself.