Mature cumulonimbus: As negatively-charged graupel descends, the electrical potential between cloud and surface builds. Eventually the electrical potential within the cloud exceeds the "breakdown potential" and channels of negatively-ionized air form in the cloud and step towards the surface. These channels are draw towards the surface by the strong cloud-to-surface potential. When negatively-ionized channels come within ~50 meters of the surface, positively-ionized channels extend upward from the surface. A negative CG "return stroke" occurs when negatively- and positively-ionized channels meet and, in this process, negative charge from the cloud and positive charge from the surface are neutralized.

Negative CGs are positive correlated with convective precipitation in space and time since both require a strong updraft and riming. Negative CGs usually strike within or near storm cores and trends in negative CGs usually follow trends in convective precipitation. The tendency for negative CGs to be collocated with heavy precipitation is fairly consistent. The tendency for trends in negative CGs and convective precipitation to be in phase is not as consistent and varies from storm-to-storm.