Well, if it's an all out *thermonuclear* exchange than most of us will not survive.
http://www.google.com/search?q=fallo...ient=firefox-a
That seems unlikely IMHO.
An Atomic attack with a 10-20 kt bomb(s) placed in a large city be a 'terrorist', ship or missile from China is more likely. In the United States the prevailing winds go west to east normally so many suggest living West or North of a large city. One problem is that a nuke from Pakistan for example might be more "dirty" than from other nations.
So if an atomic nuke went off in downtown Manhattan half the island would go boom with radiation heading towards Brooklyn or maybe Queens and Staten Island.
I'm no expert by any means and in fact there is much disagreement on not only how much radiation will fall and when it would be safe to go outdoors after an attack.
Chernobyl still has areas of Russia uninhabitable today.