Should people in the US flee to countries that aren't in the path of the radiation plumes from Japan?

Radiation has already reached hundreds of miles from the nuclear plant with just a small leak. If there is a meltdown in 3 reactors, it will be the wost nuclear disaster this world has ever seen, and the radiation will be forced eastward into the US by the Jet Stream. Maybe not levels that will lead to immediate, acute radiation deaths, but definitely cancers and long term health problems.