// BBC UK NEWS — CRONACA
Could the earliest weakening of the polar vortex on record bring UK snow?
High above the Arctic, powerful winds usually circle the North Pole each winter, helping trap some of the coldest air on Earth.
But this circulation, known as the polar vortex, has weakened and shifted position in recent days.
While such disruptions can occur during winter, scientists say an event this early in November is unprecedented in modern observations.
Similar disruptions in past years have sometimes been followed by colder weather affecting parts of Europe and North America.
However, as this is happening so early in the season, there are few historical examples to compare with and it could throw current winter forecasts into even more uncertainty.
The polar vortex develops every autumn as temperatures fall in the Arctic.
Strong westerly winds form in the stratosphere, roughly 10 to 30 miles (15-50km) above Earth's surface, locking the coldest air near the pole.
Atmospheric disturbances can cause the air high up to start warming which then makes the vortex winds weaken. This sudden stratospheric warming (SSW) can eventually lead to the strong westerlies reversing into easterly winds.
In the following days and weeks these changes can alter the position of the jet stream, increasing the chance of a blocked weather pattern where it can become drier with a colder northerly or easterly wind bringing Arctic air in.
It can also boost the possibility of snow, especially in eastern UK.