The US National Oceanic and Atmospheric Administration is calling for caution after a series of solar flares and coronal mass ejections began on Wednesday. It warns of possible disruptions in communications and other infrastructure.

Coronal mass ejections are explosions of plasma and magnetic fields from the Sun's corona, causing geomagnetic storms when they reach Earth.

NOAA says a severe geomagnetic storm is likely as early as Friday evening and could continue through the weekend.

It issued a severe geomagnetic storm watch, the second-highest such advisory on a scale of five.

NOAA says that as geomagnetic storms can affect communications, the electric power grid, navigation, and radio and satellite operations, it has notified the operators of such systems so that they can take protective measures.

It also says the storm includes the potential for aurorae to be visible over much of the northern half of the country, and possibly as far south as Alabama.

NOAA says the solar cycle is a roughly 11-year periodic change in the Sun's sunspot activity. It adds that the cycle is expected to peak this year, with another severe storm possible in the future.