If airborne radar indicates an extremely intense thunderstorm echo, what is the recommended minimum distance to avoid it?

When encountering an extremely intense thunderstorm echo on airborne radar, the recommended minimum distance to avoid it is 20 miles. This guideline is based on the potential for severe weather phenomena associated with thunderstorms, such as turbulence, lightning, hail, and wind shear, which can extend well beyond the visible precipitation.

Staying at least 20 miles away provides a safety buffer to mitigate the risks posed by the storm's severe conditions. Thunderstorm cells, especially those that are intense, can produce hazardous conditions not just directly underneath them but also at considerable distances from the storm itself due to their size and the dynamics of the surrounding atmosphere. Therefore, the 20-mile distance is considered a cautious and prudent measure to ensure safe navigation around such dangerous weather phenomena.

Other distances provided in the choices might fall short of this safety margin, making them less suitable for ensuring safety in the presence of intense thunderstorms.