I'm with Bonecruster on that. I was going to post the same idea until I saw he'd beat me to it
Winter soltice.. the longest night. All about winter and starting the journey into spring. Many real cultures celebrate this time. Dancing the life back into the world is very cool!
All the same wintery snow type things apply but plenty of dark clear stary night and shadowy edges where the dead and dormant await to be outcast by the Happy spring.