The concept of a particle balance level is worth mentioning here. The balance level is the height in the storm where a particle's fall speed equals the updraft speed. For small supercooled droplets and small ice crystals, the balance level is found at upper-levels where the updraft is weak. For large ice particles accreting rime, the balance level found at mid-levels where the updraft is stronger. In this region of the storm, ice particles are near-stationary as they collect upward-moving supercooled droplets. Riming ice particles eventually gain enough mass to fall through the updraft.

This discussion indicates that large ice particles collide frequently with both small supercooled droplets and small ice crystals. Ice-supercooled droplet collisions cause riming. Ice-ice collisions cause electrification. How? Laboratory cloud chamber studies show that electrical charge is transferred between ice particles as they collide in the presence of supercooled droplets. This ice-ice collisional charging mechanism is examined in the next section.