Supercell Collapse Phase: an example

When a supercell storm exhibits a rapid loss in the classical supercell radar reflectivity features of hook echo, Bounded Weak Echo Region and Weak Echo Region it is said to be experiencing the “Collapse Phase”. This same period is often accompanied by a general reflectivity weakening, diminishing depth of higher reflectivity, VIL, and echo top decline. In contrast, simultaniously the storm's kinematic features are intensifying. Typically the rear flank downdraft strengthens strongest shears in the mesocyclone lower toward the surface, the mesocyclone diameter itself may shrink and tornadogenesis may occur or an existing tornado may increase in size and strength.

Here, this author examines in detail a collapse phase that results in a tornado and the death of the mesocyclone as it goes through the occlusion process. The development of the tornadic circulation aloft and it's decent and arrival at the surface is examined in some detail via a nearby WSR-88D and many storm photos. Operational ramifications are also discussed.