Show the weather of clouds. The sixth paragraph is divided into levels and summarizes the meaning of each level.

Divide paragraphs and summarize the meaning of paragraphs.

The first part (1 paragraph) points out that clouds are like signboards in the sky, which explains why we can know the weather from clouds.

The second part (paragraphs 2-6): specifically introduces the morphological changes of clouds and the relationship between the gloss phenomenon on clouds and the weather, so as to explain how to understand the weather by looking at clouds.

The third part (paragraph 7): Explain the significance and limitations of knowing the weather from clouds.