How are all cloud layers and obscurations aloft classified?

Cloud layers and obscurations aloft are classified based on their ability to obscure visibility and the light that passes through them. The proper classification differentiates clouds as being either opaque, which completely blocks light and visibility, or allowing some level of translucency.

Although the term "opaque" signifies that these obscurations do not permit light transmission, it is important to understand that not all clouds or obscurations will be purely categorized this way in practical meteorology. However, when it comes to the standard classification of cloud layers in aviation meteorology, they are primarily focused on whether they obscure visibility entirely.

Translucence or transparency does come into play in some contexts, but the most significant concern when classifying clouds and obscurations aloft is their effect on visibility, which aligns more closely with being either fully opaque. Thus, the classification as "opaque" provides a clear distinction for pilots and meteorologists in understanding the impact of clouds on visibility and flight safety.