Just a random idea that I got:
What if there were more instances of certain strata when the seasons change, such as more freeze/fire during the winter/summer part of the seasons (I am accounting for hemispherical differences) and more beasts/construct/gremlin levels during the spring/fall seasons (I'm thinking of Aurora Isles etc). There could also be more undead/fiend during October for Halloween (I know about the whole promo thing, it just fits here nicely).
YOu can already do this, thats what those minerals you collect are for. You can influence what the gates will be. It is up to the player base to influence the gates. If u or everyone you know or the entire player base agreed to you can construct the gates exactly like that.
There is snow in Cooling chambers.
The whole crystal system, if several people(Hence a reason for a guild) used it they could alter it to that for that period.
Although i note how Clwn and Atrum are both somewhat missing the point, I'll have to disagree with this.
It's more trouble than it's worth, trying to change the map-weather to fit in with seasonal changes globally, IMO. Some of them won't really work either, like Fire in an Ice stratum etc.
I think that while this is a good idea, it should only be on one of the gates, so that it wouldn't affect people who don't want this. Maybe the gate could be called Stone Wheel (to show the turning of the months) or something like that.