Graupel Explained

Meteorologists have been quite right in associating graupel (sort of a flying slush) with lightning. Those two manifestations of atmospheric electricity share microphysical phenomena that contribute to conversion of heat to electrical energy. Heat is absorbed in the conversion of liquid water into water vapor. With the evaporation process, the absorbed energy becomes invested into increased molecular velocity whereby gaseous state is achieved by bringing water molecules into mutual escape velocity. Such vapor eventually absorbs atmospheric ionization, which lowers its dew point temperature. Electrical repulsion reduces intermolecular attraction to thus require additional temperature reduction for vapor condensation and for freezing of such rain.

However, charged raindrops must freeze from the inside out because only their interiors possess electrical neutrality; a provision that happens to raise ion density at their outer surfaces and advance electrical potential further toward thunderbolt production. As a matter of fact, crystallization would be impossible if intermolecular repulsion were to exceed corresponding attraction.

Up until the flash of lightning, falling ice crystals should be getting pretty wet, but their supercooled water jackets should harden up once the thunder is sounding off. Such precipitation gets a lot of attention from meteorologists; they call it graupel, and some may get paid to study it.