At what altitude should thunderstorms be avoided by at least 20 nautical miles?

Thunderstorms are highly dynamic and can produce severe turbulence, hail, lightning, and other hazards that pose significant risks to aircraft. Pilots are advised to avoid thunderstorms by at least 20 nautical miles to reduce the chance of encountering these dangers. This is particularly crucial above FL230 (Flight Level 230), which corresponds to an altitude of approximately 23,000 feet.

At this altitude and higher, the atmospheric conditions that contribute to thunderstorm development and severity can be more pronounced. Additionally, thunderstorms can generate significant updrafts and downdrafts that can extend well beyond the visible storm cloud itself. By maintaining a minimum distance of 20 nautical miles from thunderstorms, pilots can enhance the safety of flight operations by steering clear of these problematic weather phenomena that could impact the aircraft.

While thunderstorms should indeed be avoided at all altitudes for safety reasons, the specific recommendation to maintain a 20-nautical-mile distance is particularly emphasized for operations above FL230 due to increased overall turbulence and the potential for severe weather conditions at those altitudes.