At what minimum altitude do high-level clouds typically occur?

High-level clouds are typically characterized by their occurrence at altitudes starting around 20,000 feet (6,000 meters) above sea level. However, in many contexts, particularly in aviation meteorology, the classification can start at approximately 15,000 feet for specific regions.

While the clear guideline is that high-level clouds generally form above 20,000 feet, many meteorologists and aviation resources often use the figure around 15,000 feet as a practical threshold for understanding the onset of high-level cloud types, such as cirrus, cirrostratus, and cirrocumulus. Since the question is likely referring to the lower end of the high-level cloud range, the most appropriate answer aligns with the understanding that these clouds can be generally expected to be observed above 15,000 feet in the atmosphere.

This context makes 15,000 feet the best choice, as it aligns with practical meteorological classifications while acknowledging that high-level cloud observations can vary by specific geographic conditions and atmospheric profiles.