There are various ways to mark time and seasons. For starters, there's the conventional go-by-the-calendar approach. This is especially effective when looking ahead and counting down to an important, highly-anticipated event (28 days, for example).
When it comes to seasons, however, I think you've got to go by the what-clothes-are-realistic-for-today? method. By this measure, it's now winter in Seoul.
My winter jacket came out of storage today. Have a feeling I'll be keeping it close during the next four weeks.