I’m building a post apocalyptic world right. In my world, after the Nuclear War there is a brief nuclear winter.
Realistically, some have told me, the survivors would migrate south as the Southern Hemisphere would be less affected then the North. However, in my world this cannot happen under any circumstances.
See, the survivors in the North are supposed to be the ones who repopulate the continent of North America after WW3. If they leave off to Central America, there will be no one left.
What is a logical reason for survivors not to migrate south during a nuclear winter?