Weakening polar vortex may raise UK cold risk later in November

The Met Office says the stratospheric polar vortex is weakening, a development that could increase the chance of colder weather in the UK later in November, though it does not mean a cold spell or snow is certain.

Forecaster Marco Petagna said warming is taking place in the stratosphere and the vortex is starting to weaken. He said a disrupted vortex can raise the likelihood of cold weather reaching the UK, usually after a delay of several weeks.

A major sudden stratospheric warming could occur if the winds reverse direction, Petagna said. Such an event would involve a sharp rise in temperatures in the polar stratosphere and could weaken or disrupt the circulation of strong winds that helps contain cold air near the North Pole. Whether the current disturbance develops into a major warming remains a forecast, not an established outcome.

The Met Office has described the vortex as unusually stretched and linked the disturbance to stronger-than-average “wave-two” activity, in which two large atmospheric waves push into it from opposite directions. Its forecasts suggest the vortex may become increasingly displaced from the North Pole. A weakened or displaced vortex can affect the jet...