What are the chances of getting any warning? None.

What are the chances of getting out of Dodge alive with nuclear debris falling for three days or so? Slim.

Where are you going to go that a multitude of other people aren't going to and probably got their first? How far can you go on the gas that's in your vehicle tank? Nearly everyone is going to run out of fuel in the same general area. Are you going to get past them?

Suggestions:

Don't live in a big city. Look at a local map: there aren't all that many exits in any particular direction, are there? Caught in the open on the Interstate with half a million scared, frustrated people is not my idea of a picnic.

Don't live downwind from a big city.

Don't live on the main drag (interstate) out of a big city.

You're just better off not being in a place that could be attractive to terrorists. You can't escape from Mother Nature; besides, she's got a wicked sense of humor.

Sheltering in place still beats bugging out. Unless maybe you have prior knowledge of an event.

Alas, Babylon.

Sue