Agence-France Presse notes:
California is closely monitoring efforts to contain leaks from a quake-damaged Japanese nuclear plant, a spokesman said Saturday, as experts said radiation could be blown out across the Pacific.
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"At present there is no danger to California. However we are monitoring the situation closely in conjunction with our federal partners," Michael Sicilia, spokesman for California Department of Public Health, told AFP.
"California does have radioactivity monitoring systems in place for air, water and the food supply and can enhance that monitoring if a danger exists," he added.
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Experts have suggested that, if there were a reactor meltdown or major leak at Fukushima, the radioactive cloud would likely be blown out east across the Pacific, towards the US West Coast.
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"The wind direction for the time being seems to point the (nuclear) pollution towards the Pacific," said Andre-Claude Lacoste of the French Nuclear Safety Authority, briefing journalists in Paris on the Japanese crisis.
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Earlier the NRC said it was "examining all available information as part of the effort to analyze the event and understand its implications both for Japan and the United States."
The winds could shift at any time, blowing radiation into Tokyo or other parts of Japan.
However, even if the prevailing winds remain off-shore - towards California, Oregon and Washington - those American states are still a long way away. As AFP notes:
But while the great distances make the risk of radiation exposure to Californians, Oregonians and Washingtonians small, it is not zero.While US nuclear experts acknowledged the seriousness of Japan's reactor crisis, some stressed that taking steps in the United States such as distributing iodine tablets -- which prevent iodine 131 from being absorbed into the body -- would be "vastly premature."
"It's a big ocean. These (radiation) releases are essentially going to be at ground level," said Ken Bergeron, a physicist who has worked on nuclear reactor accident simulation.
"We should not confuse it with health issues in the United States."
Japan is roughly 5,000 miles (8,000 kilometers) from the US West Coast.
For example, pollution from Chinese coal factories routinely hits California. For example, Mongabay noted in 2008:
Previous studies have documented that dust from Asia — especially from deserts and industrial regions of China — routinely crosses the Pacific Ocean on prevailing winds to sully the air over the western U.S.And see this and this.
As as the Lawrence Berkeley National Laboratory wrote last December:
About a third of the airborne lead particles recently collected at two sites in the San Francisco Bay Area came from Asia, a finding that underscores the far-flung impacts of air pollution and heralds a new way to learn more about its journey across vast distances.In fact, the jet stream passes right over Japan. The jet stream was noticed in the 1920's by a Japanese meteorologist near Mount Fuji, and the Japanese launched balloon bombs into the jetstream to attack America during WWII.
In a first-of-its-kind study, scientists from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the California Air Resources Board tracked variations in the amount of lead transported across the Pacific over time.
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It’s well known that particles and other aerosols cover long distances through the Earth’s atmosphere. But the details of this transport, such as that of the lead particles’ 7,000-mile journey from the smokestacks of China to the west coast of North America, are largely unknown.
If radioactivity got blown by surface winds up into the jet stream, it could spread widely.
There are radiation monitoring networks in the U.S. While I don't know where one can view complete results, here is an example of one small system of monitors with results updated every 3 minutes (a level over 130 is dangerous). I can't vouch for it's accuracy.