Ever had a winter week that felt like the Arctic moved in overnight? The secret player is the polar vortex—a massive ring of fast winds high above the North Pole. When it’s strong and tidy, our weather stays fairly normal. But when it weakens and wanders, icy air can spill south, bringing big freezes and snow to places that aren’t used to it.
What the Polar Vortex Actually Is
The polar vortex isn’t a storm you can see on the ground. It’s a huge whirl of air that lives in the stratosphere—the layer above the weather we feel—about 15 to 50 kilometres up. Picture a spinning top of cold air sitting over the Arctic. In winter, darkness and extreme cold help it form a tight, fast “fence” of winds that keeps the cold locked near the pole.
Here’s a surprising fact: during a typical winter, winds around the vortex can race faster than a motorway speed limit—well over 150 km/h—circling the pole like a giant, invisible racetrack.
Jet Stream: The Weather’s Motorway
Closer to us, in the troposphere (the layer where clouds, rain and snow happen), flows the jet stream—a narrow river of fast-moving air about 8–12 kilometres up. The jet stream steers storms and divides cold air to the north from milder air to the south.
When the jet stream is straight and strong, weather patterns move along quickly. But when it turns wavy—looping north and south like a rollercoaster—it can drag Arctic air into mid-latitudes and park it there. That’s when you might get a week of sharp frosts, bitter winds, and snow days.
When the Vortex Wobbles or Splits
Sometimes the polar vortex gets a shock from below. Powerful weather waves push up from the troposphere into the stratosphere and disrupt the vortex. In some winters, the stratosphere can warm by tens of degrees in just a few days. This dramatic event is called a Sudden Stratospheric Warming (SSW).
When an SSW happens, the vortex can weaken, wobble, or even split into two smaller swirls. The knock-on effect often reaches the surface a week or two later: the jet stream slows and meanders, blocking highs can set up (for example over Greenland), and cold Arctic air can dive south over Europe and the UK. Not every SSW means snow for everyone, but the chances of a cold spell jump.
Sea Ice, Warm Oceans, and “Weird” Winters
You’ve probably heard that the Arctic is warming faster than the rest of the planet. That can mean thinner sea ice and warmer ocean surfaces in some areas. Warmer seas put more moisture into the air. So if a blast of cold air arrives over moisture-rich air, you can get heavier snowfall—even while the climate overall is warming.
Scientists are still investigating how shrinking sea ice and ocean changes influence the jet stream and the polar vortex. Some studies suggest that, in certain winters, Arctic warming can make the jet stream wavier, nudging cold air south more often. Other studies find the link is complicated and varies year by year. What we do know is this: a warmer world can still produce severe cold snaps, and sometimes the extra moisture means bigger snowfalls when they come.
Reading the Signs (and Staying Safe)
You don’t need to be a meteorologist to spot the hints of a coming cold blast. Keep an eye out for:
• Forecasts mentioning SSW or a weakening polar vortex in late winter.
• A jet stream forecast that dips south over the Atlantic and Europe.
• Talk of blocking highs near Greenland or Scandinavia—these can hold cold air in place.
• Local warnings for ice, snow, and wind chill—and advice from schools and councils.
Practical science helps, too. Cold, dry air robs heat from your body faster, so layer up, cover your head and hands, and protect your phone battery (they drain quicker in the cold). If you’re travelling, check conditions and carry basics like water, snacks, and a charger.
So, as winter settles in, ask yourself: if the jet stream suddenly bends and an SSW is in the news, how would you prepare for a week of icy weather—at school, on the bus, and at home? Thinking ahead is smart science in action.