Here's why. I was just re reading the comics and in Miles Behind Us a Dale said to Rick you've been with us about three months now. And it is snowing. In the Morgan and Duane special they said it had been about five months since this all started and it is December then. In Around Every Corner, it is revealed by the date on the security tapes that the Outbreak started on July 20th. So when Lee died, it was fall and on,y three months in. When Rick woke up from his coma he was five months in.