No other storm has matched it in speed or magnitude. But that doesn't mean we're not preparing for the inevitability. Despite our superior ability to predict these events, the stakes are exponentially higher in a modern, hyper-connected world.

In 1859, a giant plume of magnetized plasma was flung out into space from the Sun. This coronal mass ejection (CME), the sibling of a massive solar flare, traveled the 93 million miles between the Sun and Earth in only 17.6 hours. Today, it's known as the Carrington Event, and is remembered by the largest geomagnetic storm in the history of recorded space weather.

When the shock wave of accelerated particles arrived on September 1, 1859, the disturbances to Earth's magnetosphere were so great that telegraph communications across Europe and North America went on the fritz. Sparks leapt from telegraph infrastructure , and machinery was so inundated with electric currents that operators were able to transmit messages while disconnected from battery power. Compasses wiggled, and brilliant auroras were reportedly seen as far as the Caribbean.

According to unpublished FEMA documents obtained by Government Attic , a FOIA database and non-profit organization, the Department of Homeland Security agency once mapped out a disaster plan for the occurrence of another geomagnetic "superstorm," noting that the rare—yet "high-consequence"—scenario has "the potential for catastrophic impact on our nation and FEMA's ability to respond."

"These things tend to come in clusters, so just when you're on your knees, another one hits. They're really the only naturally occurring catastrophe that can come in these successions," James McAteer, an astrophysics professor at New Mexico State University, told me.

FEMA predicts that a geomagnetic storm of this intensity would be "a catastrophe in slow motion," though not unmitigatable. Space weather events happen all the time, and many are harmless; an event causing radio blackouts, solar radiation storms, and geomagnetic storms would be anomalous. Still, its cascading effects on power and communications would challenge FEMA's ability to respond to a nationwide crisis, thus making this exercise an important one.

First to feel the impact would be high-frequency (HF) networks, such as some aviation and long-distance military communications. As X-ray and ultraviolet radiation strike the ionosphere, a protective layer of our planet's atmosphere, changing its conductivity, it would absorb radio signals trying to bounce off of it, resulting in a blackout of HF communications, as well as some lower frequency ones, on the entire daylight side of Earth.

"What's scary are these cascading effects," Justin Kasper, professor of Space Science and Engineering at the University of Michigan, told me.

The widespread damage to North America's power grid would be unimaginable. (The interconnectedness of the grid "is almost like a biological system," McAteer said.) Transformers, which are extremely expensive to build, make power transmission possible. But when a CME sweeps across Earth, these towers, designed to handle AC currents, are instead flooded with DC currents. This may cause them to overheat, melt, or even explode , as was the case in 1989 in Quebec, Canada.

Within 20 minutes of the CME's occurrence, FEMA estimates that 15 percent of the satellite fleet would be lost due to solar panel damage. Solar radiation from the incoming storm would add "3-5 years worth of exposure" to the panels, degrading older satellites to the point of inoperability. Low orbiting satellites, such as Iridium and Globalstar, may be less affected. Cellular service would be disrupted, and a loss of GPS capabilities could complicate FEMA operations.

"The average big American city has several days of food for people to survive. We use GPS and computers and trucks to do real-time delivery now, but if you lost all power in one city, what would you do? The problem is trying to move more than 100 million people when there's no [unaffected] nearby city to evacuate to."

At the time of the CME's arrival, a G5 geomagnetic storm alert—the highest on the space weather scale—would be in full effect. Life as we know it would pause. Cellular towers would begin to fail. Anything reliant on local power, from your cellphone charger to critical infrastructure, would be inoperable. This includes "last mile" communications as well, such as cable TV or internet.

A separate, 2008 report from the National Academy of Sciences (NAS) theorized that a "moderately severe" geomagnetic storm could leave 130 million Americans without power. According to FEMA, power grids on the the east and west coast of America would be hardest hit.