Your Most Likely Scenario

[BeardyMan]

Obviously it's going to be easier if you have a 4x4.

But back to the thread....

Natural:

Freak weather
EMP from solar storm

Man Made:

Financial collapse
America sticking their nose in somewhere else where it's not warranted or welcomed and starting WW3 (but they'll undoubtedly blame someone else). Probably Syria as they're determined to remove Assad, even though the Russians are positive that it was the rebels that used the chemical weapons. Still, that doesn't fit nicely with the war-mongers in Washington, so that'll be ignored.