Thunderstorm formation, illustration. As warm moist air rises it condenses and forms a cumulonimbus cloud. Some of this moisture may be released as rain (right). Strong convection currents will carry the moisture higher (left), where it will collide with and stick to supercooled water and other particles. When these particles become too heavy to be supported by the air currents they fall as hail. This movement of water particles cause electrical charges to accumulate within the cloud, with positive charges accumulating at high and low altitudes and a negative charge accumulating at mid altitudes. When the accumulated electrical charge becomes large enough it is discharged as lightning (lower frame). Lightning can occur within the cloud or between the cloud and the ground (in either direction).