As a longstanding sufferer from Seasonal Affective Disorder (SAD, aka the winter blues) I can tell you that within a day or two of winter solstice I can tell the days are starting to get longer, regardless of the fact that winter solstice coincides closely with the onset of the winter season. Funny how one's body is able to tell things like that. Within a week or two the blues begin melting away, despite snow on the ground, etc... for a couple more months before it actually becomes hospitable outside again.