A sunspot cluster as wide as 16 Earths has shot out at least five eruptions of magnetic fields and solar plasma, several of which may merge to create a “cannibal” solar storm in Earth’s atmosphere this weekend.

The event prompted the National Oceanic and Atmospheric Administration to release its first G4-level Geomagnetic Storm Watch since 2005. NOAA classifies solar storms on a five-point scale, with G4 representing those that are “severe.” Severe solar storms can cause voltage surges in the power grid and affect satellite and high-frequency-radio communications. Operators in these industries have adaptations to protect their equipment during these storms, says NOAA space weather scientist Rob Steenburgh. These protections can include backup systems and radiation shielding, as well as temporary changes in operations. The potential new storm could make itself known to the public, however, via colorful auroras that would be visible from the northern part of the continental U.S.—and possibly in southern states, depending on the storm’s strength. The G4 watch is in effect starting at midafternoon today.

“We are expecting to see this activity persist through Sunday,” Steenburgh says.

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