In May 2024, officials from NASA and about 30 other U.S. government agencies met to rehearse their response to an imaginary geomagnetic storm. On May 10 the real one arrived, the first G5 storm in more than two decades, and it is now the closest preview of what the next big solar storm could do.<\/p>\n\n\n\n
“The plan was to run through a hypothetical scenario, finding where our existing processes worked and where they needed improvement,” said Jamie Favors, director of NASA’s Space Weather Program at NASA Headquarters in Washington. “But then our hypothetical scenario was interrupted by a very real one.”<\/p>\n\n\n\n
G5 is the top level on NOAA’s five-step scale. The storm was later named for space weather physicist Jennifer Gannon, who died that year.<\/p>\n\n\n\n
A coronal mass ejection, or CME, is a cloud of charged gas and magnetic field thrown off the Sun. NOAA’s Space Weather Prediction Center, or SWPC, puts their speed anywhere from under 155 miles per second (250 km\/s) to about 1,860 miles per second (nearly 3,000 km\/s).<\/p>\n\n\n\n
“The fastest Earth-directed CMEs can reach our planet in as little as 15-18 hours. Slower CMEs can take several days to arrive,” the center writes.<\/p>\n\n\n\n
The last and best look comes from DSCOVR, a NOAA satellite at a point called L1, about 1 million miles (1.6 million kilometers) toward the Sun. SWPC says it “can often provide 15 to 60 minutes advanced warning of shock arrival at Earth.” It is also the moment forecasters learn which way the cloud’s magnetic field points. Storms grow stronger, SWPC notes, when that field turns “more pronounced and prolonged in a south-directed orientation.”<\/p>\n\n\n\n
Forecasters saw it coming. Ahead of the storm, NOAA issued its first severe geomagnetic storm watch in almost two decades, according to NASA’s one-year review.<\/p>\n\n\n\n
For utilities, the trouble starts on the ground. Swings in Earth’s magnetic field push a near-direct current into long power lines, and NOAA says that can saturate transformer cores, heat their insides and “cause protective equipment elsewhere in the grid to trip when it shouldn’t.”<\/p>\n\n\n\n
The grid got through it. NASA’s one-year review says the Gannon storm “did not cause any catastrophic damages.”<\/p>\n\n\n\n
There was still damage. NASA’s one-year review<\/a> reports that some high-voltage lines tripped and transformers overheated. Over the ocean, many trans-Atlantic flights swung south to spare passengers and crew extra radiation and to avoid losing communication and navigation near the North Pole.<\/p>\n\n\n\n The surprise came from the fields. The storm disturbed the ionosphere, the charged upper layer that GPS signals must cross, a known solar risk to satellites and navigation<\/a>. Some Midwest farmers lost GPS guidance while they were planting corn.<\/p>\n\n\n\n According to NASA, “certain GPS-guided tractor models veered off course or stopped working, disrupting or delaying planting for many U.S. farmers.”<\/p>\n\n\n\n Terry Griffin, a professor of agricultural economics at Kansas State University, has tried to put a price on it. “Not all farms were affected, but those that were lost on average about $17,000 per farm,” he said in NASA’s review. “It’s not catastrophic, but they’ll miss it.”<\/p>\n\n\n\n Quebec, March 13, 1989. NOAA’s account says Hydro-Qu\u00e9bec’s grid went down within 90 seconds and six million people spent nine hours without power.<\/p>\n\n\n\n Malm\u00f6, October 30, 2003, about 50,000 customers for an hour. A 2005 paper led by Antti Pulkkinen blamed geomagnetically induced currents, or GIC, and found that “the primary mode of GIC-related failures in the Swedish high-voltage power transmission system were via harmonic distortions produced by GIC combined with too sensitive operation of the protective relays.”<\/p>\n\n\n\n Then 1859, the Carrington Event, when telegraph operators reported fires from sparking equipment. Some far older storms are known only from traces, like the solar storm of 993 recorded in tree rings<\/a>.<\/p>\n\n\n\n Ready.gov<\/a>, the federal government’s preparedness site, warns that space weather can disrupt power lines and even cause “widespread power outages.” Its advice before a storm includes keeping the car’s gas tank at least half full, because gas stations rely on electricity to power their pumps, and keeping “extra batteries or external chargers” for phones, laptops and other small electronics.<\/p>\n\n\n\n During a storm, it asks people to keep electricity use “as low as possible,” which can help power companies avoid rolling blackouts, and to follow Emergency Alert System instructions. The harmless side of these storms is the auroras, the same kind of lights a NASA astronaut has filmed from orbit<\/a>.<\/p>\n\n\n\n Several coronal mass ejections from the same active region merged on the way, NASA says, forming the superstorm that reached Earth on May 10.<\/p>\n\n\n\n By luck, NASA’s STEREO-A spacecraft sat between Earth and the Sun that week, about 4 million miles closer to the Sun than L1. A study led by Eva Weiler of the Austrian Space Weather Office in Graz found it could have predicted the storm’s strength 2 hours and 34 minutes earlier than a spacecraft at L1.<\/p>\n\n\n\n In July 2026 a team led by Nithin Sivadas of NASA’s Goddard Space Flight Center argued the worst storms may hit up to twice as hard as previously thought, because extreme solar wind readings taken at L1 tend to overstate what actually strikes Earth, which made Earth’s response look capped. “We usually assume the truth may be around its measurement. But probability theory says it leans one way. That’s why space weather risks appear underestimated,” Sivadas said.<\/p>\n\n\n\nFarm tractors exposed a weak spot<\/h2>\n\n\n\n
Older storms did knock out power<\/h2>\n\n\n\n
Households are told to plan for an outage<\/h2>\n\n\n\n
Earlier warnings and a ceiling in question<\/h2>\n\n\n\n