How cold is too cold to go for a walk?

backinpgh

What do you think? We only have one car, which DH takes to work during the day. So the only way I can get out of the house is to walk or take the bus. It's starting to get chillier and I wonder at what point we should just hibernate for the winter. She has a snowsuit and all kinds of other warm clothing, but what should the limit be?