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The main thing to keep in mind with winter driving is that it can take longer (sometimes MUCH longer) than at any other time of the year. One has to slow down anytime there is white stuff on the roadways, and should really be prepared to just pull off the road and spend a night curled up in a motel if things get really bad. Beyond those basics, we offer a number of tips on winter driving and links to real-time weather conditions. Our editor has also written this article which distills it all down. I suspect that your girlfriend already knows much of this, but a refresher is never out of order.
AZBuck