You may need to use a shovel or an ice pick to get your car out of the snow, but once you do you'll want snow tires (or even better, snow chains) to keep it on the road. An organization called the Rubber Manufacturers Association actually sets the guidelines for officially labelled snow tires. These tires ideally require rows of large grooves that start at the tire's edge and wrap toward its center. Also, if 25% of the tire's surface area has grooves it will getter better traction in snow. The RMA have another designation for "Severe Snow Use," where the tire must meet requirements set by the American Society for Testing and Materials that exceed routine tire traction performance.