Weather story or question?
Lightning strikes in this file photo. (Pexels)
Q: Astrid. We had a lightning strike in South Nanaimo that came from a clear blue sky. The only storm was 10 kilometres away in North Nanaimo which we couldn't even see! So question is... How far away from a thunderstorm can lightning strike? Rick.
A: Lightning can actually strike a long way away from a thunderstorm, but only certain types of lightning can reach areas that are many kilometres away from the original thunderstorm.
Believe it or not, we don’t fully know how lightning is produced. What we understand is that inside a thunderstorm ice particles swirl around and collide with each other. When this happens, electrical charges separate. Ice crystals that are positively charged rise to the top of the thunderstorm, while those with negative charges (including hail stones) sink to the bottom of the storm. As the storm moves, the negatively charged lower part of the cloud alters the charge at the surface, encouraging positively charged particles to gather along the ground.
Next, the negatively charged part of the storm at the bottom of the cloud sends a charge to the ground. It doesn’t have to actually reach the ground for the magic to happen. As long as the charge is close to the surface positively charged objects will be attracted (opposites attract, right?) and a channel will develop. The electrical transfer in the channel is the lightning we see.
Ninety to ninety-five per cent of all lightning strikes are negatively charged. The others are positively charged, meaning they originate in the upper, positively charged part of the storm cloud. Positive lightning is particularly dangerous because of its ability to strike a long way away from the core of the storm; it can strike either ahead of the system or behind it, up to 5 to 10 miles or 8 to 16 kilometres away from the storm, and in areas that might not be considered at risk of a lightning strike.
Now, here’s where the thunder comes in. It makes sense that when lightning strikes, it heats the air around it at an explosive speed. Fun fact: for a brief moment, lightning can raise the air temperature by more than 25,000 degrees Celsius! Amazing. The heated air itself is what causes thunder. Light travels faster than sound so the flash is seen first, before the sound waves reach the target and thunder is heard.
Spring storms can be quite exciting when they develop on Vancouver Island. Unlike in other parts of Canada, thunderstorms aren’t a regular thing on the island so it’s really important to take heed of the warning “when thunder roars, go indoors!” Even if you think you’re a long way away from a thunderstorm, lightning can still strike in your area.
With all this in mind, it’s sounds like what you witnessed was a positive lightning strike many kilometers away from the actual storm itself.