What defines a layer in terms of clouds or obscuring phenomena?

A layer in cloud terminology refers to clouds or obscuring phenomena that have bases at approximately the same level. This means that the cloud cover is relatively uniform across a horizontal plane, creating a distinct layer that can impact visibility and flying conditions. This uniformity is essential for pilots and meteorologists as it affects flight operations and the interpretation of weather reports.

In aviation, knowing whether clouds form in layers or are scattered plays a crucial role in understanding weather phenomena. A layer typically indicates a more stable environment where the clouds do not drastically vary in height, which assists in predicting weather conditions.

The other options mention variations in height or characteristics that do not align with the standard definition of a cloud layer. For instance, clouds with widely varying bases or only opaque clouds do not fulfill the criteria for being classified as a layer. A more comprehensive understanding of cloud types emphasizes the importance of consistent base levels in defining cloud layers.