Northern lights are expected to illuminate Ottawa's sky Friday evening as a powerful geomagnetic storm ushers in the weekend.

On Thursday, the U.S. National Oceanic and Atmospheric Administration's Space Weather Prediction Center (SWPC) issued a geomagnetic storm alert in anticipation of this rare event.

Geomagnetic storms are classed by severity from G1 (minor) to G5 (extreme). The upcoming storm is classified as a "severe" G4, according to the SWPC. It's the first G4-level alert declared by the agency since January 2005.

Robyn Fiori, a scientist with Natural Resources Canada, said the storm actually arrived in Ottawa around 1:30 p.m. Friday.

"I definitely think there's a chance that we'll still see some Aurora tonight, and it's also possible that activity will reduce during parts of the day and then maybe start up again [Saturday] night," Fiori said.

The sky over Ottawa is expected to start clearing around 7 p.m. and clear completely by 11 p.m., according to Environment Canada.

Fiori advises Ottawa residents interested in viewing the northern lights to get out of the city and find an area of clear sky with minimal light pollution.

"The Aurora is something you can actually see from quite far away. In some cases, you can see it when it's up to 3,000 kilometres away from you, so your exact location isn't quite as important as the sky just being clear and the light pollution being reduced," Fiori said.

Fiori said geomagnetic storms typically last from one to six hours, but based on observations, this particular storm is predicted to last longer.

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