A typical lightning flash can heat the surrounding air to about 30,000 kelvins.
This extreme heating occurs as an electrical discharge rapidly travels through the atmosphere. The channel expands explosively when its air is heated, producing the pressure wave heard as thunder. The visible flash may contain several separate strokes along the same channel.
The figure is often compared with the Sun’s surface temperature, which is about 5,800 kelvins, but lightning is much hotter for a very brief interval. It does not mean the entire thunderstorm reaches that temperature; the intense heat is confined to the narrow lightning channel.
Lightning can occur within clouds, between clouds, or between a cloud and the ground. Thunder is delayed because sound travels far more slowly than light, allowing observers to estimate distance from the time between the flash and the sound.