Warning of Winter is a poem Bilbo Baggins recites when he, Frodo Baggins, Peregrin Took, Meriadoc Brandybuck, Sam Gamgee, and Gandalf are discussing the Council of Elrond and the upcoming journey to Mordor. Bilbo observes that they will be travelling in the winter because Frodo waited until his birthday to start his journey to Rivendell.

When winter first begins to bite

and stones crack in the frosty night,

when pools are black and trees are bare,

'tis evil in the Wild to fare.