Definition
The initial, faintly luminous discharge of ionized air that advances downward from a thundercloud in a series of short, jagged steps, creating the conductive channel along which the main lightning stroke will travel.
Plain English
The first, dim path of electrified air that pushes down from a thundercloud in short jumps, building the channel that the bright lightning bolt then follows.
Context Anchor
Seen in aviation weather study when learning how thunderstorms produce lightning.
Derivation
Called a 'step' leader because it does not travel smoothly — it advances in short, distinct segments of roughly 50 metres at a time, pausing briefly between each step before continuing toward the ground.
Why Pilots Care
Lightning can damage aircraft structure, avionics, or fuel systems, so recognizing the conditions that produce step leaders helps pilots avoid storms.
Grounding Statement
Picture a faint, branching trail of ionized air feeling its way downward from a thundercloud in tiny hops — once it reaches the ground, the bright return stroke flashes back up along that same path.
Intuition Check
A step leader is not a person leading steps, and it is not a flight procedure. It is part of the physical process that creates lightning.
Example Sentence 1
The instructor explained that the bright flash a pilot sees is actually the return stroke, which travels back up the channel first carved out by the step leader.
Example Sentence 2
The pilot diverted twenty miles around the cell after the radar showed rapid vertical growth associated with step leader activity.