How does the author use metaphor in the epic, The Cattle Raid of Cooley?

The author uses a famous extended description that functions essentially as a metaphor using the messenger/interpreter, watchman/interpreter technique. Mac Roth, Medb's messenger reports a scene of unnatural phenomena that functions as a metaphor of the army of Ulster since Fergus is able to read these phenomena for what they really are.... the effects of the army of Ulster on the march.