According to NASA, the storm is related to a sunspot the sun of Jupiter — eleven times the size of Earth.
The storm was expected to be most severe Friday, though experts said they didn't anticipate problems with communication networks.
"This is not a super solar storm," said Larry Combs, a space weather forecaster with the National Oceanic and Atmospheric Administration's Space Environment Center in Boulder.
So far, the storm has interfered with airline communications and radio communications for teams on Mount Everest, Combs said. But problems were not widespread.
The storm, called a "coronal mass ejection," is a mass of solar gas that swept toward Earth at 2 million mph. The usual cycle for such a storm is every 11 years; this one was expected to hit three years ago.
"It is kind of like a snowstorm in June in Colorado," Combs said.
Combs said power companies, which are among the center's best customers, have been notified and were taking precautions to avoid voltage problems and blackouts.
"We will be watching our transmission system very closely 24 hours a day," said Steve Roalstead, spokesman for Xcel Energy, a major Western power provider.
Satellites also are at risk during such storms but cell phones aren't likely to be affected unless they rely on satellites, Combs said.
"Satellites are built to live out there, but an accumulation of hits can cause problems," he said.
Operators can shut them down and put them in what is called a "stow" position until storms pass. They may need to be boosted back up to their correct altitudes after the storm.
Much like predicting a hurricane, forecasting the impact of a geomagnetic storm is difficult.
"It could just strike a glancing blow or hit head on," Combs said.