July's broiling heat and wind-driven storms are big risks for power outages from the dry desert southwest to the swampy East Coast. Outages are usually local, with downed lines leaving us in the dark for a few hours or perhaps a day. But what are the chances of something worse happening? What if the entire U.S. power grid went kaput?

Many experts say that's an unlikely event. The nation's power grid is a complex, yet technologically advanced, system with plenty of backup. But scenarios do exist that could lead to such a massive failure: a solar flare, a cyberattack, or even just a series of unfortunate events -- also known as a cascading failure.

"It is conceivable," said Ian Dobson, professor of engineering at Iowa State University who focuses his research in preparing for just that possibility. "If there is a series of failures, then the grid doesn't have sufficient redundancy to transmit electricity and the load is shed, that is a blackout and the lights go out."

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If it's a just a matter of rebooting the system, that can be done in a couple of hours, explained Dobson. But if there's physical damage to high-voltage transmission lines, substations or other infrastructure, it could take weeks or months to replace and repair transformers or other equipment.

Modern society without electricity would obviously be a tough place to live. Electricity keeps clean water running, communications operating, food cold, hospitals open and our homes and streets safe. Most backup systems, like diesel generators, are only designed to run for a few days.

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Government and industry officials appear to be most worried about temporary, regional blackouts, the kind that happened along the East Coast in 2003 when a software malfunction tripped the power for 45 million U.S. residents in six states, and another 10 million Canadians.

Human error -- a decision by a technician to cut a high-voltage line between two substations -- led to a 12-hour blackout for 6 million people in California, Arizona and Northern Mexico. Sewage pumps failed, spilling contaminated water onto beaches, and food spoiled in thousands of groceries.

Our grid is fairly stable.iStockPhoto

Experts say a continent-wide failure would require some kind of physical damage to the power system: something like a massive solar flare -- the so-called "Carrington event" of 1859 -- that caused telegraph wires to fry worldwide and led to visible auroras in places like Cuba and Jamaica.

"There has been some modeling that says (a similar event today) could cause significant damage to electronics," said Mark Weatherford, principal at the Chertoff Group and former security chief for the North American Electric Reliability Corporation, a non-profit regulatory group responsible for maintain power.

"This is something that has not gone unnoticed," Weatherford said. "Industry and government have been very active to understand the implications that the threat would cause."

In recent years, manufacturers have looked at ways to protect transformers from solar events, shunting high-voltage lines into the ground so they aren't damaged and figuring out ways to isolate troubled substations from the main grid.

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Protecting against cyberattacks is an ongoing battle. Just last week, a new report by Symantec warned of serious threats to electric grids from "Dragonfly," a group of hackers likely based in Eastern Europe who have launched malware to disrupt power supplies, industrial control systems and other kinds of infrastructure. Weatherford said the weak link is the companies that provide software to utilities.

The hackers infiltrated industrial control vendors, who then issued updates and patches with contaminated software that were uploaded by utilities.

"It is a concern and there's a lot of people looking into this right now," Weatherford said.

Thinking about the unthinkable -- at least when it comes to a massive power outage -- is a good exercise for engineers like Iowa State's Dobson. He says that the United States has ignored fixing infrastructure like the power grid for too long, even though the possibility of a widespread catastrophe is low.

"The power grid is a complex machine, and everything east of the Rockies is all tied together," Dobson said. "There's good reason to have such a large power grid, to back each other up, but it also has a vulnerability and occasionally you can have a cascading failure."

Weatherford says the U.S. grid is not likely to fail. There are too many ways to isolate trouble spots. But if things go south, you might want to consider moving to Texas. The Texas power grid is self-sustainable for power generation and distribution.

"Texas," Weatherford said, "could probably disconnect and be fine on their own."