The storm rated as a G4 on a NOAA scale, which tops out at G5. It's the strongest storm that's happened in the current solar cycle, which lasts about 11 years.

The Space Weather Prediction Center says that the storm is from sun activity that started on March 15.  Two magnetic eruptions occurred in quick succession. They combined into one larger eruption before intersecting the Earth's orbit on Tuesday.

The storm arrived earlier (10 a.m. EDT) and was stronger than predicted. The storm could last 24-36 hours.

 It warned that there could be possible widespread voltage control problems at power systems and some protective systems could trip out key assets from the grid but that appeared to not be happening.