What kind of scene does the first two sentences of Shan Yu's poem describe?

The first two sentences of this poem describe the scenery of the forest: all night, the stars and the moon meet, the forest is clear, there is no cloud and no thunder, and the weather is fine. Pave the way for the surprise of the author's last two sentences.

Mountain Rain

Weng Juan

It was white all night, without clouds or thunder.

Pingming suddenly saw a stream running and knew that it was raining from another mountain.