Stratospheric Warming Weakens Polar Vortex, Raising UK Cold Odds
A warming high in the stratosphere is weakening the polar vortex, the Met Office says, raising the chance of UK cold later in November. What it can and cannot tell us.
Air high above the Arctic is heating up, and the Met Office says the polar vortex in the stratosphere is starting to weaken as a result. For the UK, that shifts the odds toward cold weather, though the forecaster says any effect usually shows up a few weeks later and is far from guaranteed.
Met Office forecaster Marco Petagna pointed to the second half of November as the period when an influence is more likely, if one comes at all. A University of Reading meteorologist added that this event is unusual, which makes it harder than normal to anticipate a cold spell.
What is happening in the stratosphere
The polar vortex is a band of strong winds that circles the North Pole each winter. It sits in the stratosphere, the layer of the atmosphere above the one where our day-to-day weather forms. When that layer warms quickly, meteorologists call it a sudden stratospheric warming, and the winds of the vortex can slow down.
According to Petagna, a warming of this kind is under way now. He said it raises the chance of cold weather in the UK, normally a few weeks down the line, which puts the most likely window deeper into November.
BBC Weather described the usual chain of events: a disturbed vortex can allow northerly or easterly winds to carry Arctic air toward Britain, bringing drier and colder conditions. That pattern raises the chance of snow, especially in eastern areas.
Why a warming does not always bring cold
The link between the stratosphere and the weather on the ground is a matter of probability. Petagna noted that a major warming event happened last November and did not lead directly to much cold weather in the UK. In his words, it “just increases the chance of it occurring.”
Professor Andrew Charlton-Perez, a meteorologist at the University of Reading, said the typical response to a sudden stratospheric warming is colder and drier weather over Europe and the UK. He also said scientists have not seen an event quite like this one before, so a cold spell is harder to anticipate at the moment.
What the official forecasts say for the coming weeks
The Met Office long-range forecast for Nov. 21 to Dec. 5 points to unsettled conditions. The forecaster says it is too early to say whether there will be snow over Christmas.
For the week ahead, BBC Weather expects low pressure to bring rain to the southeast, with colder conditions following in the second half of the week.
Weather maps from WXCHARTS, which are computer model output and not an official forecast, show snow reaching the Scottish Highlands on Nov. 21 and lows of -4C in Scotland on Nov. 13. Model runs this far ahead often change from one update to the next.
What it means for people in the UK
A weakening polar vortex can tilt the pattern toward cold air from the north or east, with a delay of a few weeks. The Met Office message is that the chance of cold has gone up, without any certainty that it will arrive. Last November’s major warming is a recent example of an event that did not deliver much cold to the UK.
Charlton-Perez’s point that this warming looks unlike earlier ones adds another layer of uncertainty to the outlook for late November and early December.
Readers in the UK should follow updates and any warnings from the Met Office and their local authorities as the forecast for late November becomes clearer.
Source: Daily Express
