The literal device used in the north wind whispered mournfully is personification.
Personification is a type of figure of speech which is used to define a non-human object or idea with the attribute of a human. It also used to define a speech when a writer symbolizes a person with a quality. This literary tool is used in many of the novels and we all use it in our day to day speeches unconsciously.
In the given sentence, the north wind is compared to a person who is mourning. This sentence may be used to define an upsetting situation. The sound of the wind is personified as mourning of a person.