“Forecasters at the NOAA Space Environment Center in Boulder, Colo., observed a geomagnetic storm on Sunday, May 15, which they classified as an extreme event, measuring G-5 — the highest level — on the NOAA Space Weather Scales. […]

Possible impacts from such a geomagnetic storm include widespread power system voltage control problems; some grid systems may experience complete collapse or blackouts. Transformers may experience damage.”

NOAA /.