Figure 2. Depiction of how a vortex tube contained within westerly environmental shear is deformed as it interacts with a convective cell (viewed from the southeast). Cylindrical arrows show the direction of cloud-relative airflow, and bold solid lines represent vortex lines with the sense of rotation indicated by circular arrows. Shaded arrows show the forcing influences that promote new updraft and downdraft growth. Vertical dashed lines represent regions of precipitation. (a) Initial stage: Vortex tube loops into the vertical as it is pulled into the updraft. (b) Splitting stage: Downdraft forming between the splitting updraft cells tilts the vortex tubes downward, resulting in two vortex pairs. The barbed line at the surface marks the boundary of the cold air speading out beneath the storm. (Adapted from Rotuno 1981)