TrendPulse|Northern lights forecast: Why skywatchers should stay on alert for another week

Space weather forecasters are TrendPulsewatching closely as the massive sunspot that produced last month's spectacular aurora display continues to rotate across the sun. The spot will be in Earth's sight for another week or so, forecasters said Thursday, meaning this specific "window of opportunity" for potential aurora viewing only has a few days left.

So far the sunspot, now known as region #3697, has produced nothing that could lead to a significant or widespread aurora on Earth. If it does, skywatchers will only get a few hours' or a day's notice – one of the limitations of the difficult art of predicting where and when the northern lights will appear.

"3697 is still relatively large and magnetically complex, meaning it's certainly capable of producing intense solar flares, and most importantly, the coronal mass ejections needed for aurora," Bryan Brasher, a project manager at NOAA's Space Weather Prediction Center, told USA TODAY in an email Thursday. "It should rotate away from view in the next week or so."

Geomagnetic storm needed

In order for aurora to be visible across the U.S., Brasher said a significant geomagnetic storm is needed. "To approach the aurora sightings we saw last month, where they are visible across large parts of the continental US, you'll need a strong (G4) or extreme (G5) geomagnetic storm," he said.

Geomagnetic storms are produced by solar flares and coronal mass ejections from the surface of the sun. They're more common when sunspots appear on the sun's surface.

Extra-strong sunspots can trigger auroras but also pose a danger to satellites, airplanes, GPS navigation and the power grid.

Folks usually don't have much time to prepare for the aurora. Typical aurora displays are forecast with only a few hours' advance notice, but large ones like last month's were generated by a solar explosion that could be seen by forecasters days before it splashed across Earth's atmosphere.

Highest sunspot number in 22 years

The average sunspot number for May 2024 was 172, the highest value in 22 years, according to astronomer Tony Phillips of SpaceWeather.com. The higher the number, the more sunspots there are.

"So far, June is even higher at 200. If this continues for the rest of the month, June could log the highest sunspot counts since Dec. 2001, rivaling the peak of potent Solar Cycle 23," he said.

The sun goes through 11-year-long cycles, which alternate between so-called "solar maximums" and "solar minimums." As of the middle of 2024, we are nearing the solar maximum of Solar Cycle 25, when solar activity will be at its highest.

Solar maximum is almost here

"While there are currently no geomagnetic storm watches, we are approaching the period in the Sun's 11-year cycle of maximum activity ("solar maximum"), which we expect to occur sometime between now and the end of the year," Brasher told USA TODAY. 

With that in mind, we can expect elevated chances for geomagnetic storms for at least the next couple of years, he said. "So while we have nothing forecasted for the next three days that makes me think that there will be widespread aurora viewing across the lower 48, anyone hoping to catch a glimpse should have several more opportunities, particularly in the northern tier, to see the aurora."

Astronomer Tony Phillips was even more optimistic: "The May 10th superstorm may have been just the first of several magnificent displays we experience between now and 2026," he told USA TODAY in an email.

Contributing: Trevor Hughes, USA TODAY