Bomb cyclone: What is the weather phenomenon slamming B.C. and U.S.? – National

More than half a million Americans and 100,000 British Columbia residents were without power on Wednesday morning as they grappled with a weather phenomenon known as a “bomb cyclone.”

The powerful storm swept across the northwest U.S., battering the region with strong winds and rain, causing widespread power outages and downing trees, killing at least one person.

In B.C., highways closed, trees were downed and many remained without power Wednesday.

But what is a bomb cyclone?

Global News chief meteorologist Anthony Farnell said the phenomenon is not new.

“This is something that has recently become very popular on social media, but it’s actually a meteorological term that has been around for decades,” Farnell said.

Meteorologists Fred Sanders and John Gyakum gave this pattern its name in a 1980 study.

A bomb cyclone is a large, intense mid-latitude storm that has low pressure at its centre, weather fronts and an array of associated weather, from blizzards to severe thunderstorms to heavy precipitation.

According to the U.S. National Oceanic and Atmospheric Administration (NOAA), bombogenesis, a term used by meteorologists, occurs when a mid-latitude (the latitudes between the tropics and polar regions) cyclone rapidly intensifies, or strengthens, over a 24-hour period.

“When you have a rapidly intensifying cyclone that deepens 24 millibars in 24 hours or less, so about a millibars per hour, that would be a bomb cyclone. This more than doubled that. In fact, it almost tripled it — 66 millibars in 24 hours,” Farnell said.

Bombogenesis can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters, according to NOAA. It is popularly referred to as a bomb cyclone.

Most cyclones don’t intensify rapidly in this way.

Bomb cyclones put forecasters on high alert, because they can produce significant harmful impacts.

According to Reuters, the U.S. Eastern Seaboard is one of the regions where bombogenesis is most common. That’s because storms in the mid-latitudes – a temperate zone north of the tropics that includes the entire continental U.S. – draw their energy from large temperature contrasts.

Intense cyclones also require favourable conditions above the surface. Particularly strong upper-level winds, also known as “jet streaks,” and high-amplitude waves embedded within storm tracks can help force air to rise.

When a strong jet streak overlies a developing low-pressure system, it creates a feedback pattern that makes warm air rise at an increasing rate. This allows the pressure to drop rapidly at the centre of the system. As the pressure drops, winds strengthen around the storm. Essentially, the atmosphere is trying to even out pressure differences between the centre of the system and the area around it.

Experts are warning that extreme weather events are likely to get more frequent as the climate continues to change and warm.

Ryan Ness, director of adaptation at the Canadian Climate Institute, said lowering greenhouse gas emissions and adapting for the future need to go hand in hand.

“We need to prepare for a future where these kinds of events are more common and more intense. And that means building up our infrastructure. It means ensuring that we’re protecting areas from flooding, like along B.C.’s coasts,” Ness said.

“The return on investment in adaptation is actually very high. It can seem like a costly investment upfront to build a bridge so that it’s one and a half times higher to let water pass underneath it, for example. But the cost of not having the cost of replacing that bridge, if it washes out, is obviously so much higher.”

–With files from Reuters