I'd leave the car and build an igloo. It is better insulated than your car. If well made you can even light a fire inside.

This, provided that you don't go out, farther than the nearest supermarket with just a t-shirt on you,

Under severe weather conditions you should plan to be prepared for the unexpected. If nothing happens, good for you, but if it does, you will not regret those extra boxes in the trunk.

Keep there a couple good blankets, a small petrol stove and minimal cooking gear, high energy food like chocolate will keep you alive and warm for a good while.

A small shovel and a knife should already be there, eh?

D.