The use of terms including “atmospheric rivers” and “bomb cyclones” to describe weather phenomena has moved out of scientific journals and into the mainstream in recent years, but meteorologist Cindy Day says there’s nothing alarmist about the language.
Day says that when used appropriately, such scientific language is necessary and can help people better prepare for the impact of extreme weather events.
Her comments come as British Columbia’s coast braces for intense winds brought by a bomb cyclone, a non-tropical storm system caused by a rapid drop in atmospheric pressure at its centre.
Environment Canada warns it could bring gusts of 120 km/h to the central and north coasts, with winds of 100 km/h or more elsewhere on the coast and Vancouver Island.
It says the storm could cause downed trees, travel delays and power outages, with the peak of the storm expected tonight and severe weather likely to continue into Wednesday.
Day says the term “bomb cyclone” has been used by scientists for decades and describes “a low-pressure system that is undergoing explosive cyclogenesis,” or the creation of cyclonic air circulation.
She says terms like “bomb cyclone” and “atmospheric river” can often help paint a picture that allows people to better understand and prepare for various weather systems.
In British Columbia, an atmospheric river originating near Hawaii has long been known as a “pineapple express.”
“So, an atmospheric river — right away, people start to think, ‘OK, it’s a narrow band of moving water,’” Day said.
“It does give you the sense that this is going to be a steady event and that there’s not going to be time for the ground to absorb the rain. It’ll continue to rain and eventually cause flooding because of that concentrated rainfall.”
In British Columbia, the government called for the creation of a scale to rank the power of atmospheric river events in 2021, in the wake of a devastating system that brought widespread flooding and shut down the Trans-Canada Highway and other key roads.
But Environment Canada said the next year that implementing such a scale for public warnings was premature.
Day noted that she had received “a lot of grief” for using the term “bomb” in relation to meteorological phenomena, with some accusing her of trying to sensationalize weather events.
“I really believe that if they’re used in the proper context, that they’re not alarmist,” she said.
“As long as the people know that they’re getting their information from a qualified source, and that source (or) that person is using the terms correctly and not shouting out ‘bomb’ every time there’s an area of rain coming in, I think it’s really important to understand those words and to take them seriously and to know that they’re based in meteorological fact, in science.”
A series of meteorological terms associated with extreme weather have become popularized in recent years. Here’s how some of them are defined by the American Meteorological Society:
BOMB CYCLONE
A storm outside the tropics in which central pressure drops rapidly, by a certain amount within a certain period of time, with this varying according to the latitude. A larger pressure drop to qualify as a bomb cyclone is required at higher latitudes in the process, referred to as “bombogenesis” or “explosive cyclogenesis.” The American Meteorological Society cites a 1980 paper that calls it a “predominately maritime, cold-season event, often with hurricane-like features.”
ATMOSPHERIC RIVER
A long, thin, horizontal “corridor” of water vapour typically associated with a low-level jet stream ahead of the cold front of a cyclonic storm outside the tropics. Atmospheric rivers are associated with heavy precipitation in places where they are forced upwards and they transport more water than double the flow of the Amazon River, on average.
HEAT DOME
A mass of exceptionally warm air trapped under upper-level high pressure. The pressure causes a doming effect by preventing the hot air from rising and preventing the development of clouds and rain. In some cases, sinking air from the upper-level high pressure produces further warming due to compression. The phenomenon can last several days, creating calm and stagnant conditions.
POLAR VORTEX
The “planetary scale” circulation of air around the north and south poles in mid to high latitudes. A paper in the Bulletin of the American Meteorological Society says there are two polar vortexes, one in the higher stratosphere and one in the lower troposphere. It says outbreaks of extremely cold air at ground level are most directly related to movements in the edge of the tropospheric polar vortex.
