US skywatchers could be in for a rare sight: The northern lights could be seen as far south as Pennsylvania over the next several days amid the potential for a strong geomagnetic storm. Beginning Sunday, the sun sent out various bursts, including multiple coronal mass ejections, or CMEs, which Live Science describes as "explosive jets of solar material." Several are headed our way, including two that are expected to collide to form a cannibal CME event—basically "a giant, combined wavefront that, upon reaching Earth, triggers a powerful geomagnetic storm," the outlet explains. This should happen on Thursday, according to the National Oceanic and Atmospheric Administration.
A CME already hit Earth on Wednesday, triggering a moderate geomagnetic storm—rated G2 in severity on a scale from G1 to G5—in Herzogswalde, Germany, which sits at 51ºN latitude. The stream of particles interacting with gases in the Earth's magnetic field triggered auroras seen from the city through clouds and urban lights, per CBS News. But Thursday's storm is expected to be rated G3 in severity or strong.
"A G3 storm has the potential to drive the aurora further away from its normal polar residence, and if other factors come together, the aurora might be seen over portions of Pennsylvania (41ºN), Iowa (42ºN), to northern Oregon (44ºN)," according to NOAA's Space Weather Prediction Center. The best estimates for when and where northern lights might appear are typically issued 30 to 90 minutes beforehand, the outlet notes. A short-term forecast can be found on SWPC's website. Another moderate geomagnetic storm is predicted for Friday. (Read more aurora borealis stories.)