While it is true that snakes are typically less active in winter, this is not always the case. Sometimes it just appears that a snake or some other animal is hibernating when they really may not be. Snakes do not actually hibernate in the winter like bears or other animals, but rather they become much less active and rarely seen by humans.
Sometimes snakes will find a stump hole to slither into until an unseasonably warm day, crawling out to enjoy the warmer weather. Typically though, snakes are not very active in the colder winter months throughout the year.