Arctic air over Western Canada has sent temperatures plunging. What you need to know about the polar vortex
Plus, what causes Arctic outflow, and how Arctic air can escape the jet stream
If the frigid temperatures across British Columbia have you feeling like you're in the Arctic, your instincts aren't all wrong.
The polar vortex bringing freezing conditions to parts of the province originates in the North Pole — meaning that freezing air you're feeling on your face is quite literally from the Arctic.
Here's what you need to know about the weather phenomenon.
What is the polar vortex?
The polar vortexes are large areas of low pressure and cold air high in the atmosphere that constantly swirl around both the North Pole and South Pole.
Closer to the surface, these vortexes are surrounded by the polar jet streams — relatively narrow, rapid streams of wind in the upper atmosphere that encircle the poles and usually keep cold air trapped.
But every couple of years the polar vortex is disrupted, splitting into multiple "lobes" that extend south. That disruption also causes the polar jet stream to weaken, which can help push and hold the freezing air over parts of Canada and the US.
"What we're experiencing right now and what happens a couple of times a winter, is when that vortex weakens a little bit," said June Skeeter, a postdoctoral fellow in geography at the University of British Columbia.
"You can think of it as holding the cold air in, and when it weakens a little bit the cold air can kind of move out of where it normally is."
Right now, a polar vortex lobe is sitting over much of B.C. and the Prairies, bringing colder-than-usual temperatures.
What is the difference between the polar vortex and Arctic outflow?
Environment Canada also issued an Arctic outflow warning for much of British Columbia's coast.
While polar vortex refers to the large system of cold air sitting high over the region, Arctic outflow refers to the surface-level winds now passing over the coast.
The outflow is described by Skeeter as "very cold air from the Arctic that has moved its way down here, and is kind of parked on top of B.C. and Alberta. We call it an outflow warning because cold air is very heavy and dense, and so it wants to sink. It flows kind of the same way water might and sinks down."
Darius Mahdavi, CBC's science and climate specialist, explains the winds are whipped up because "Arctic air wants to make it out to the Pacific. This can cause winds blowing 60 to 80 kilometres per hour, which is why the wind chill is such a problem for the coast."
Why is the polar vortex disrupted?
Even though the polar vortex is strongest in winter, it can be disrupted by certain patterns in the upper atmosphere. According to the U.S. National Oceanic and Atmospheric Administration, those patterns can become more common in late winter during El Niño years.
La Niña and El Niño are two opposing climate patterns that affect winters in Western Canada. This winter has seen an El Niño weather pattern, bringing generally warmer, milder conditions throughout December and early January.
This is partly because El Niño usually causes the polar jet stream to shift further north, locking away more of that Arctic air. But thanks to waves generated in the upper atmosphere, El Niño can also disrupt the polar vortex. That, in turn, can cause the jet stream to become more wavy, pushing Arctic air further south.
Skeeter said weather is "quite random and chaotic," making it difficult to draw direct links between broad weather events.
"But speaking in general terms, strong contrast between the ocean and land temperatures is one of the things that can cause the jet stream to weaken," they said.
The cold weather is expected to continue in B.C. for much of the weekend, with temperatures only rising to –6 C in Vancouver on Saturday.
Environment Canada said the wind chill will likely ease Saturday afternoon but it could still make it feel like –10 C to –20 C through Sunday morning in Metro Vancouver.