A powerful geomagnetic storm is underway that could trigger intense northern lights tonight

Get ready to pull out your cameras: There's a geomagnetic storm underway, and it could produce the northern lights across the country.

The National Oceanic and Atmospheric Administration's Space Weather Prediction Center (SWPC) has called for a major geomagnetic storm that was anticipated to hit Earth Thursday and into Friday, and it's already begun.

A geomagnetic storm is a disturbance of the Earth's magnetic field, typically triggered by solar activity on the sun.

On a scale of G1 to G5, the SWPC predicted a G4, which was reached earlier Thursday afternoon. For comparison, the geomagnetic storm that occurred on May 10-11 was a G5.

But the caveat, as always, is that the northern lights are difficult to predict.

For example, last week the SPWC had forecast a G3 storm for the weekend after two powerful solar flares erupted from the sun, followed by a coronal mass ejection, which sends particles from the sun on a fast wind towards Earth. If these particles interact with our magnetic field, we get the northern lights.

Initially, however, it looked like it was a miss. A few days later, though, the northern lights could be seen as far south as South Dakota and other parts of the U.S.

"We have a fair amount of confidence in our timing and intensity," Shawn Dawl, the service co-ordinator for SWPC said in a press teleconference on Wednesday about today and tomorrow's potential, and it looks like their forecast was fairly accurate.

But for the northern lights to happen, a lot of things have to line up. 

"If you think of two magnets and they have the same polarity and you try to put them together, they repel; if they're opposite, they connect, and the magnets will stay together," Dawl explained. 

"Same thing here: if that magnetic field in the [coronal mass ejection] is the same as Earth's we'll have an initial impact and effect and immediate enhancement and geomagnetic response no doubt, but we probably will not reach to those severe levels or or potentially higher.

"If it's favourably connected ... then we will escalate in in responses, and that's where the true potential will come in."

Powerful geomagnetic storms, albeit beautiful, also have the potential to disrupt power grids, as was seen in Quebec in 1989.

That served as a lesson to power companies around the world, which have since taken measures to prevent such disruptions in power lines.