Slitherine

Is it possible for sever winter to start on a mud turn in November or does it have to be winter?

This questoin is for the 3.0 version. Thanks

It can start at any turn regardless of the current weather.

In my example, would mud affects still apply during the ussr turn? Or does it switch to winter?

If the severe winter hits then it switches to severe winter (not regular winter). Severe winter has its own effects on units and terrain.