A “strong geomagnetic storm” means faint auroras might be visible in Canada and northern United States cities Thursday night, though experts say you shouldn’t expect power grids and communications to be disrupted much.

A powerful geomagnetic storm is poised to descend over Earth on Sept. 16, potentially bringing aurora borealis to regions like Pennsylvania, Iowa and Oregon, the National Oceanic and Atmospheric Administration announced — but it appears that some Californians were already lucky enough to witness it just outside their doorstep last week.