Cumulonimbus

The thunderstorm cloud, a massive vertical development cloud extending from near the surface to the tropopause or higher, often with a characteristic anvil-shaped top. Cumulonimbus clouds produce extreme hazards including severe turbulence, hail, lightning, heavy rain, microbursts, wind shear, tornadoes, and icing at all levels. The FAA recommends maintaining at least 20 nautical miles of separation from a cumulonimbus cloud, and flight through or beneath one is extremely dangerous for any aircraft.