The rhyme:

"If the sun shines on Groundhog Day; Half the fuel and half the hay."

The reason:

February 2 is Groundhog Day in the United States and Canada. During the festival if the groundhog emerges from its burrow and talks to members of the Inner Circle. If it fails to see its shadow winter will soon end. If the groundhog sees its shadow, it will return into its burrow and winter will continue for 6 more weeks.

Punxsutawney Phil is the most famous of all groundhogs – it's his prediction which traps Bill Murray's character in Punxsutawney, Pennsylvania, USA in the classic film 'Groundhog Day'. However, there is little evidence to support the groundhog's predictions in real life, as only the Inner Circle can translate what Phil is saying.