Thunderstorms seem to avoid cities, drifting by just outside of range. There may be something of an explanation to that.
If you've ever noticed that it seems rare for a thunderstorm to make it into town, you aren't imagining it. It's a real phenomenon. The catch is that it isn't a consistent phenomenon.
Natalie Hasell, a warning preparedness meteorologist for Environment and Climate Change Canada, offered her insights into what is known about why thunderstorms dodge around cities, and why it isn't a 100 per cent guarantee it will happen.
"Just because you live in a city doesn't mean you're protected or safe by this weird thing," said Hasell. "The thunderstorms still make it to cities."
In fact, plenty of the precipitation a city receives in a year is from thunderstorms. A lot of the damages you see in a given year caused by natural occurrences are thunderstorm related, be that with hail or wind, or even lightning strikes.
"People need to take all the precautions that they would normally take in a thunderstorm scenario [in a city]," said Hasell. "Because there is no actual 'magic dome' or anything like that around the city, but there are some things that cities do."
One of the things cities do that cause this strange occurrence is disrupting the landscape. Towering skyscrapers, apartments, and even suburbs change how the wind is able to move through the landscape, causing the wind to divert around these tall structures, and even creating pseudo wind tunnel conditions between them.
An additional factor is the fact that cities are made up of mostly concrete and asphalt. These dry materials generate a lot of heat, changing the temperature of a city. Cities tend to be a few degrees warmer, varying a few degrees based on the size of the city.
"So the sun heats the ground, the ground heats the air at the bottom, and it becomes buoyant and starts the upward motion all by itself," details Hasell.
The resulting effect is a current of air circulating around the city. This current can split incoming storms before they can glide over town.
While this can deflect the incoming thunderstorm on occasion, on other occasions, it can do the opposite, and fuel a storm. This is where the inconsistency comes from.
If there is a lot of moisture in the city, due to maybe leftover puddles from a previous bit of rain, or maybe everyone watering their lawns, it can lead to a storm. The warm air carried up by the wind tunnels and upstreams caused by the taller buildings can draw a hot, moist air column up that can feed a forming storm.
"As I've already said, people to still cater to the fact that thunderstorms are in the forecast," said Hasell. "If something looks pretty dangerous wherever people happen to be, please seek shelter."
The factors that build these artificial effects are more prominent in larger cities but can happen anywhere with enough paved surfaces. Even in a smaller town or city, the chances of weather developing and changing course rapidly aren't outside the realm of possibility.