In response to post #23150429.People have discussed this and 100% sure it is impossible to change seasons without disabling/enabling mods. I know even Bethesda worked on that for Skyrim and could never get it to work properly. Just one of those things that they may have for us in Elder Scrolls VI.
So if I could get it to work, it would be that much more exciting, yes? I love proving people wrong...
Load this up. Go somewhere in the Riverwood area (I picked meshes specifically from this area to test). Console "set gamemonth to 1"
Then start walking towards Whiterun... and while you're at it, try picking some flowers or crops in the farms when you get there. Because those things grow so well in the winter, you know?
This is a proof of concept, but I'm working on an SKSE plugin for the same functionality to get around some of the major Papyrus limitations. I'm not including psc source because it's utter crap.