Polar Vortex

Sky News, BBC One and 5 News reported that changes to the polar vortex, linked to sudden stratospheric warming, could raise the chance of colder weather in the UK this winter. The polar vortex was described as a ring or donut of strong winds high over the Arctic that can weaken, wobble, reverse or split, allowing cold air to sink and disrupting the jet stream. Sky News and BBC One said the changes appear to be happening unusually early this year, and Sky News said forecasters are in uncharted territory.

BBC One and Sky News noted that a strong El Niño may be influencing the timing. BBC One reported that the impact is particularly uncertain because the event is early in the season, and that a typical warming event would increase the chance of cold and potentially snowy weather later in winter. It also reported that a long period of blocked flow could reduce rainfall and affect drought-hit areas in southern England. Sky News reported that models suggest high pressure could allow freezing Arctic air to move into parts of North America and Northern Europe, but said the early timing made extreme outcomes less certain than a midwinter event such as the 2018 Beast from the East.

5 News reported that forecasters expected unusually cold, snowy and windy conditions this winter, and described the sudden stratospheric warming as the earliest on record. Its interviewee said the link to UK cold weather is not automatic and depends on pressure patterns and the jet stream, with any cold spell typically following about six weeks later. BBC One said that if the warming is major it would be the earliest on record, while Sky News said it was the earliest such event on record and that a polar vortex collapse this early in winter had not been seen before.