Anyone who's ever lived in SoCal will be familiar with the Santa Ana Winds. This is a weather phenomena that happens in the Fall and early Winter in which the wind direction changes. Instead of the typical sea breeze coming off the ocean the air you get is a hot, fast, dusty wind coming from the Mojave Desert.
http://en.wikipedia.org/wiki/Santa_Ana_wind

In a typical year the Santa Ana winds contribute to forest fires, brown skies (from the dust) and high air conditioner use. But the events at the end of season 3 have added a new problem, radioactive fallout from Fort Irwin.

I don't think that the fallout from one nuke will make the area uninhabitable, and it won't kill the surviving humans outright. But it will increase the risk of cancer among the survivors, and birth defects among their future children. And it might damage, or destroy any crops they manage to grow at the Colony. And who knows what it will do to the Zombies. We already know that, unlike humans, the Little Ones are actively mutating. How is radiation going to impact that?

So, how is this added complication going to effect the story going forward?