Polar Vortex Explained — Why Cold Air Plunges South

What Is the Polar Vortex?

The polar vortex is a large area of low pressure and cold air that circulates around the Arctic (and Antarctic) pole. It sits in the stratosphere, about 15-50 km above the surface, and is always there — not just during cold snaps.

How It Normally Works

When the polar vortex is strong, it keeps cold air locked tightly around the pole. The jet stream flows in a relatively straight west-to-east path, acting as a fence between Arctic and mid-latitude air.

What Happens When It Weakens

Sometimes the vortex weakens and wobbles, often triggered by sudden stratospheric warming events. When this happens:

1. The jet stream becomes wavy
2. Arctic air spills south through the waves
3. Mid-latitude regions experience extreme cold snaps
4. Meanwhile, the Arctic may actually warm up temporarily

Famous Polar Vortex Events

The January 2019 event sent temperatures in Chicago to -30°C (-22°F) with wind chills below -50°C. Schools, businesses, and mail delivery shut down across the Midwest.

Is Climate Change Making It Worse?

This is an active area of research. Some scientists hypothesise that rapid Arctic warming is weakening the polar vortex more frequently, leading to more extreme cold outbreaks in mid-latitudes. Others argue the evidence is not yet conclusive.

What It Means for You

When weather reports mention the polar vortex, prepare for a significant cold snap lasting several days to a week. Stock up on supplies, protect pipes, and dress for extreme cold.

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