This study examines several kinematic mechanisms of size sorting that occur in many convective thunderstorms. These mechanisms are analyzed through observations of convective storms (including mesoscale convective systems and supercell thunderstorms) as well as simple numerical models. The size sorting mechanisms discussed in this paper include differential sedimentation, updrafts and downdrafts, strong rotation, and vertical veering of the wind. The latter mechanism results in a low-level signature in ZDR known as the ZDR arc. Through a simple, explicit microphysics numerical model we show that the ZDR arc is proportional to the storm-relative environmental helicity (SREH) and that it might indicate storm severity and potential for tornadogenesis. With the anticipated polarimetric upgrade of the NEXRAD WSR-88D network in mind, operational applications and the importance of such microphysical observations are discussed.