Cirrus cloud tropopause prevents the warm, moist air forming the thunderstorm from rising any higher, thus creating the flat top. In the tropics, these thunderstorms occasionally produce copious amounts of cirrus from their anvils. High-altitude winds commonly push this dense mat out into an anvil shape that stretches downwind as much as several kilometers. Individual cirrus cloud formations can be the remnants of anvil clouds formed by thunderstorms. In the dissipating stage of a cumulonimbus cloud, when the normal column rising up to the anvil has evaporated or dissipated, the mat of cirrus in the anvil is all that is left. Contrails
Altostratus undulatus cloud elements that have stretched through the sky. They often run parallel, but can also appear to interweave across the sky, especially if dual wave systems are seen (also referred to as biundulatus). Gravity waves aligned normally to the direction of the wind can show wide, near-parallel cloud strips. Altostratus undulatus cloud The altostratus undulatus is a type of altostratus cloud with signature undulations within it. These undulations may be visible (usually as "wavy bases"), but frequently they are indiscernible to the naked eye. These formations will generally appear in the early stages of destabilizing return flows, especially over the southern