When we moved all the reptiles into the one room, We blocked off access to the window.
(It also keeps nosy people from looking in)

It does not matter, snakes can feel the changes in barometric pressure and other factors that change with seasons.

This can be observed by noting behavior changes when a rain system moves in.

Rain equals abundant food to garters, even if you keep them indoors from birth, they can tell when its going to rain.

So it stands to reason that snakes could sense the change of season without any direct exposure.
(humidity levels change, air pressures, air density, etc..)