Shit, I drove up there from San Fran to Truckee and theres no way in hell I'd go on those roads with out chains in the snow and I've been driving in some of the worst new england weather my whole life.
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MS6 has no clearance, so if there is lots of fresh snow and no tracks do not even bother. MS6 is a fair winter vehicle but it is not a great one: you need much more clearance and skid plates if you want a real winter/snow car. In fact, I recommend studded tires if they are allowed in your neck of the woods.
However, I am certain that studs are a no-go in the Bay area! If I was driving to Tahoe every week, I would get a truck based SUV like a 4Runner (I am biased) and put some serious off-roady but narrow tires on it. If you are unfamilar with skidding and sliding, take a lesson, it might save your life! Good stability control is also key to survival...
However, I said it before and I will say it again: go for an ice tire! Did you know that snow tires typically do worse on ice than most all seasons? I am currently running Michelin LTX which are very good on ice but only do ok in snow. I have driven right after a 2 foot dump and the vehicle did ok. If it snows more, you should just wait it out if you life is worth a dime, they will clear the roads within a few hours...
I cant tell you how many times I saw Bay area dorks (no offense) with BMW x5's stuck in the snow bank around the lake...
SUV drivers often give away their advantage by driving like there is no snow. 4x4s do not brake much better than regular vehicles... Dorks do not count!
Personally, I am still more worried about ICE! I grew up in AB!