I'm on some 18" Blizzak WS70s. On the flat in about that much snow below.... it was slow driving with traction control kicking in constantly ( but smoothly ). I use to own a e90 335xi, and made a conscious decision to get RWD this time even though one year in my e46 I got stuck going up Avenue just south of St. Claire. It was about 15cm of snow. When I had AWD, it never snowed much and now, murphy's law.... it does!
Anyway, it was said before, eco-pro helps and the extra weight helps and the right WS tires too. Hills with packed snow/ice as a base the are problems.
Now for everyone who doesn't know TO and believes it doesn't get much snow... you are right. Not much at all. The problem is that the city is too cheap to buy enough equipment and plays the waiting game with nature to see if it will all melt. That causes the hard packed stuff to form and then new fresh layers come down ontop of that if you aren't lucky. This is why I bought WS - for those occasional snowfalls and of course ski trips.
Get the equipment etc ( use eco pro, tires, weight ) and know your limits so you don't get stuck and know when to avoid which roads.
Actually this applies to AWD too - some people think its literally unstoppable, but soon find out its not.
Current: F87 M2 MT MPE, E84 PP SP LP
Previous: F30 - 335i AT, E90 - 335xi MT, E90 - 330i MT, E46 - 330i MT