What could be a sign of an impending storm with respect to cloud types?

The presence of cumulonimbus clouds is a significant indicator of an impending storm. These clouds are characterized by their towering structure and can extend high into the atmosphere, often leading to severe weather events such as thunderstorms, heavy rainfall, hail, and even tornadoes. The development of cumulonimbus clouds usually indicates instability in the atmosphere, which is conducive to storm formation. Their presence can prompt air traffic controllers to be vigilant, as they can create hazardous flying conditions due to turbulence and severe weather phenomena.

Other cloud types mentioned, like cirrus, typically indicate fair weather or a change in the weather pattern, while a sudden increase in haze may signal approaching moisture but does not directly indicate a storm. Stratus clouds generally suggest overcast conditions but are less associated with severe weather compared to cumulonimbus clouds. Thus, the formation of cumulonimbus is a clear alert for pending storm activity.