1.The fog is not permanent it moves it stays only for a moment as in the last sentence it moves on.
2. D a metaphor it using the cat as a metaphor for the fog.
It is a Christian allegory.
Please show us all 3 sources.
This is not actually about nature it’s meaning nothing good can stay. In the outsiders this poem is used. When Johnny dies he says stay gold to Ponyboy meaning stay good.