Northern lights were visible in the Pittsburgh area tonight

PITTSBURGH (KDKA) – The Northern Lights could be visible in western Pennsylvania on Friday.

First Alert meteorologist Ray Petelin says it's possible but not guaranteed. The Pittsburgh area typically scores close to 8 on the K index, which measures the strength of geomagnetic storms. Friday we'll be at about 6 or 7, he says.

There was a chance that the Northern Lights would be visible on Thursday, but on Friday the probability is even higher. The K index will likely be too weak to see them on Saturday.

When the Northern Lights are visible in western Pennsylvania, look for a dark spot on the northern horizon. It's a good idea to give your eyes some time to adjust to the darkness.

The Northern Lights have graced the Pittsburgh area a few times this year. Both the Aurora Borealis and the Perseid meteor shower were visible one night in August and created a dazzling celestial spectacle. Green, purple, red and pink hues were also visible in the skies over western Pennsylvania already in May.

What causes the Northern Lights?

When a geomagnetic storm occurs, the solar wind is sent to Earth. Charged protons and electrons follow the Earth's magnetic field and penetrate the Earth where the magnetic fields are weakest: at the poles. The electrons collide with the various molecules that make up our atmosphere, creating a dazzling play of colors in the sky.

It is rare for the Northern Lights to be seen so clearly this far south. Most of the time we're lucky if it even happens once a year.