WHEN the Met Office warns of a polar vortex it's not good news for heat-lovers.
Here is what the weather phenomenon means.
What is the polar vortex?
A polar vortex can lead to the arrival of extremely low temperatures.
It is a mass of desperately cold air that sits above the Earth’s north and south poles.
This dense, cold air is controlled by a large pocket of low pressure, which rotates in an anti-clockwise direction at the North Pole and clockwise at the South Pole.
A band of strong winds high up in the atmosphere - up to 30 miles above Earth - keeps bitterly cold air locked around the Arctic region.
The winds regularly exceed 155 miles per hour.
How does a polar vortex happen?
The term "vortex" in itself refers to the anti-clockwise flow of air helping to keep the colder air near the North Pole.
The air moves in a clockwise direction at the South Pole.
The polar vortex strengthens and weakens during winter.
When it undergoes changes and moves south, it can create alarmingly cold conditions.
A strong polar vortex needs a strong jet stream, and gives stormy, wet weather.
A jet stream is a narrow band of strong wind in the upper levels of the atmosphere.
A weak polar vortex tends to lead to a weaker jet stream, which results in northerly or easterly winds in the UK bringing cold air from the Arctic.
A weak vortex can split into two or more freezing vortices, covering a wide area including the US, Canada and Europe.
The phenomenon associated with wintry weather is known as a Sudden Stratospheric Warming.
When was the last polar vortex?
In January 2023, Met Office forecasters warned of high-altitude polar vortex winds in Scotland.
The winds are forecast to significantly weaken, resulting in a weakened jet stream which could see Arctic air plunging towards Scotland in a February freeze.
The Beast from the East in 2018 was the last time Britain saw a polar vortex with freezing temperatures and bitter winds.
At least 17 people across the UK died in the weather event.
In January and February 2019, Chicago was one of the places worst affected by the polar vortex.
The wind chill brought temperatures down as low as -29C, nearly 10 degrees colder than the 1985 record.
Windchill temperatures reached -60C - colder than Antarctica.
At least 21 people died across the country during the polar vortex-induced weather, according to Reuters.
In fact it was so cold railway engineers had to set fire to train tracks to keep them from
Does the polar vortex happen every year?
It always exists near the poles, but weakens in summer and strengthens in winter.
People in the UK will rarely hear about a polar vortex unless it is heading towards them.
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