The northern lights may glow low on the horizon overnight from Saturday, April 18, into Sunday, April 19, across as many as 20 northern U.S. states, as NOAA space weather experts forecast a G1 or G2 geomagnetic storm. The best chances run from Alaska through northern Washington, Idaho, Montana, North Dakota, South Dakota, Minnesota, Wisconsin, Michigan and Maine.
That is the window for skywatchers who want to see the aurora without traveling far north, though the display will depend on how the storm develops and whether skies stay clear. If a G2 storm materializes, the reach could extend farther south into Oregon, Wyoming, Nebraska, Iowa, Illinois, Indiana, Ohio, New York, Vermont and New Hampshire.
NOAA said G1-G2 minor to moderate geomagnetic storming levels are expected on April 18 as negative-polarity CH HSS geomagnetic conditions persist. Active to G1 minor levels are expected to continue through April 19, followed by unsettled to active conditions on April 20 as HSS effects linger. A new moon on April 17 should help by making the sky darker.
The aurora forms when solar wind interacts with Earth’s magnetic field, and in this case the flow is being energized by a high-speed blast from a hole in the sun’s corona. Aurora-chasers often watch the Kp index, but Bz is the more important measure for whether a display can actually brighten and hold together. For anyone hoping to catch it, the key night is April 18 into April 19, and the answer to whether the lights reach deep into the Midwest and Northeast depends on how strong the storm becomes.