I am amazed that this was never mentioned when I was in school. Of course it should have been obvious…. The days are lengthening or shortening as quickly as they can. At the solstices, as slowly as possible. So spring and autumn are the times when the change is the quickest.
Rather like Groundhog day is nearly midway between the winter solstice and the vernal equinox. Not quite but close. So with 12 weeks of winter, of course there are about six more weeks of winter on Groundhog Day. The only scandal is that the joke is not quite on the right day.