Cumulus Rotation: Model and Observations of a Waterspout-bearing Cloud System

Intense cumulus rotation has been found to precede severe tornadic storms. Substantial advances in documenting and understanding precursor conditions for destructive tornadic vortices have been made using Doppler radar observations. A typical tornado-associated “mesocyclone” has a diameter of 5–10 km, tangential wind velocities 15–25 ms-1 and vorticities in the neighs borhood of 10-2 s-1. Only about 60 percent of these strong meso-cyclones produce funnels, however, suggesting that a special juxtaposition of a number of conditions is required.