Northern lights alert as rare G4 geomagnetic storm hits United States

Northern lights in the sky in Sterling Heights, Michigan, after a G4 solar storm in 2024. Photo / Salwan Georges, The Washington Post

Northern lights may be visible in swathes of the United States on Monday night (local time), including in places unusually far south, after a powerful X-class solar flare ejected from the sun at the weekend.

A key Nasa model showed the magnetic shock wave called a coronal mass ejection, or CME, may be stronger and faster than originally modelled. It began to slam Earth’s magnetic field on Monday afternoon (eastern time), its impact probably sparking a wave of auroral displays.

A storm of this strength could allow aurora to be visible to the naked eye at least as far south as parts of California, the central Plains and the Mid-Atlantic. There is potential for lights even south of those locations.

Long-exposure photos – even on cellphones – would also be able to capture such an event at more southerly latitudes. Places such as Southern California, Texas and the Deep South would be included, with some potential for the lights to dip into Mexico or beyond.

In response to the latest outburst from the sun, the National Oceanic and Atmospheric Administration’s Space Weather Prediction Centre issued its highest alert for geomagnetic storm potential. It calls for a severe storm, or a G4 out of a maximum 5.

“Watches at this level are very rare,” the centre wrote. A G4 storm was confirmed to be impacting Earth about 3pm on Monday.

There are inherent uncertainties to the show – like whether the bulk of the CME hits Earth head-on or only grazes the planet. The early arrival of the storm could also mean less of the show occurs after dark – though available data does not yet suggest that will be the case.

The solar flare

This is all associated with an X2-class solar flare, which launched off the sun about 11.09am Eastern time Sunday. It originated from sunspot 4341, a large bruise-like discolouration on the surface of the sun, throbbing and pulsating with magnetic energy.

In addition to their enhanced magnetism, sunspots are unstable and cooler regions on the sun’s surface.

Solar flares are flashes of light and electromagnetic radiation that expel high-energy particles through space at the speed of light. This particular flare caused a degradation of radio wave propagation and partial radio blackout over western South America and the eastern South Pacific.

It comes as the sun continues to be near its solar maximum, an 11-year cycle on average. Sunspots are at their greatest concentration during these maximums. They are a primary cause of CMEs and solar flares.

The last significant outbreak of aurora occurred in November.

The geomagnetic storm

The solar flare was followed by a CME. CMEs are slower waves of magnetism and ejected solar plasma that surf through space like a shock wave. They typically take one to three days to reach Earth, if pointed in our direction. But as it’s already reached Earth, this is a very speedy CME.

Stronger CMEs are usually faster than weaker ones.

The timing may be ideal for much of North America and Europe. At least in some places, skies may illuminate in the hours after sunset.

CMEs interact with Earth’s magnetic field, transforming potentially harmful energy and magnetism into visible light – the aurora. Colours of the aurora are caused by the energy interacting with oxygen and nitrogen, among others, at high levels of the atmosphere.

How to view

To maximise visibility, get away from city lights and find a clear, unobstructed view of the northern horizon. Check the weather forecast first, too.

With much of the Lower 48 currently free of major weather systems, clear or partially cloudy skies should dominate much of the land. Areas that may experience the most clouds are generally near the Mexico border and into Texas and other parts of the South. Cloudiness may also favour the border with Canada, especially near the northern Rockies and Great Lakes.

Your best bet will be to look northward a couple of times per hour after dark through at least midnight.

Social media and space-weather-related websites often deliver a critical heads-up.

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