Solar storm heading for Earth – northern lights possible over Canada on the night into Tuesday 20 October

The best chances are in Yellowknife and Edmonton. There, the northern lights may climb high enough to be seen with the naked eye if the sky is dark and clear.

In Winnipeg, it may appear as a greenish glow or red pillars low in the sky towards the north.

In Vancouver and Montreal, it is most likely that only a phone camera in night mode will catch it. The camera gathers light for several seconds and sees colours the eye cannot.

Kp is a global three-hour average. The northern lights come in waves, and an outburst can last ten minutes or two hours, so patience pays off.

Clear or nearly clear skies are expected in Toronto and Montreal. Edmonton, Winnipeg and Vancouver look set for partly cloudy skies – a few gaps in the cloud can be enough. Thick cloud is expected over Yellowknife and Halifax for most of the night, so the chances there are slim. Cloud cover is Skycastor's forecast for the dark hours. It is updated continuously, so check again closer to the time.

Find a dark spot with an open view to the north. Street lights and the glow of towns swallow the faint colours, and just twenty minutes out of town makes a big difference.

It is dark enough from about 19:29 until 06:35.

Good dark places include Jasper, Wood Buffalo, Mont-Mégantic and Kejimkujik.

Give your eyes 15–20 minutes to adjust to the dark, and avoid looking at your phone screen in the meantime.

Try your phone's night mode, or a camera on a tripod with a 5–15 second exposure. The picture often shows stronger colours than the eye can see.

Auroras form when electrically charged particles from the Sun hit Earth's magnetic field and are channelled down into the atmosphere around the poles. At 100–300 kilometres up, they collide with oxygen and nitrogen, which light up – oxygen in green and red, nitrogen in blue and violet.

That corresponds to a minor geomagnetic storm, G1 on NOAA's scale from 1 to 5.

The Kp index runs from 0 to 9 and shows how disturbed Earth's magnetic field is. At Kp 3, the northern lights are usually seen only in northern Norway, Lapland and Iceland. From Kp 5 they can reach Denmark, Scotland and northern Germany, and at Kp 8–9 they have been seen as far south as southern Europe.