The Northern Lights will light up the sky on Friday. Will they be visible in Illinois? –NBC Chicago

The sunspot cluster that lit up Chicago-area skies with the northern lights three weeks ago will return this weekend, but the prospect of seeing the northern lights in the city this time remains unclear.

The National Oceanic and Atmospheric Administration is forecasting a moderate geomagnetic storm in the Northern Hemisphere Friday evening and early Saturday, causing the northern lights to extend farther south than usual, perhaps just reaching the edge of northern Illinois.

The solar storm is not expected to create as bright a spectacle as the northern lights seen in the Chicago area three weeks ago.

A category G2, or moderate activity, storm watch has been issued for this weekend. In early May, NOAA issued a G4 watch for severe activity, but the storm resulted in G5 levels, or extreme activity, which is the top of the scale, according to NOAA.

“It is not unusual for a sunspot cluster as complex as this to maintain its strength for weeks,” said Erica Cei, a spokeswoman for NOAA’s Space Weather Prediction Center. “The reason we are seeing a return of activity now is that the sunspot cluster responsible for the activity in early May has returned to view from Earth. The rotation of the sun takes approximately 27 days.

The Space Weather Prediction Center said the northern lights could be visible in the northern Midwestern states between Idaho and New York.

A forecast of the Northern Lights can be found at swpc.noaa.gov.

The northern lights, which occur almost constantly in the planet’s two polar regions, are caused when coronal mass ejections of solar material from the sun reach the Earth’s magnetic field, causing a geomagnetic storm. Neon lights are produced by collisions between solar material and atoms and molecules in Earth’s upper atmosphere.