There does not seem to be a single event in Poe's life from which he based his enduring poem, "The Raven." Many people assume that the Lenore mentioned in the poem is a reference to Poe's own wife, Virginia (much in the same manner as his equally memorable "Annabel Lee"). However, Poe wrote the poem two years before Virginia's death, so the symbolic reference is unlikely. According to one source, "The Raven" may have been influenced by several other works, including
“Lady Geraldine’s 1843 Courtship” by Elizabeth Barrett Browning; Barnaby Rudge by Charles Dickens; and two poems, “To Allegra Florence” and “Isadore” by Thomas Holly Chivers.
Poe discusses the creation of the poem in his essay, "The Philosophy of Composition."
... he describes the poem as one that reveals the human penchant for “self-torture” as evidenced by the speaker’s tendency to weigh himself down with grief.
In the essay Poe also discusses his method of composing “The Raven.” He claims to have given much thought to his selection of the refrain, recognizing in it the “pivot upon which the whole structure might turn.” His selection of the word “Nevermore” came after considering his need for a single, easily remembered word that would allow him to vary the meaning of the lines leading up to it. The poem uses this refrain, or variations of it, as the closing word for each stanza. The stanzas become increasingly dramatic as the speaker makes observations or asks questions that reveal his growing tension and diminishing reason.
As for the use of the word December, it is the first month of the winter season, and nights are the longest of any other month, perhaps "creating a mood of mystery."