The polar vortex can break much earlier than expected: what is it and how can it affect Catalonia?

BarcelonaMeteorological models are beginning to outline an unusual scenario for this time of year: the possible breakdown or a very significant alteration of the polar vortex. Forecasts from the main models – such as the European ECMWF – point to a very pronounced weakening of this structure during the first days of November that could end up modifying the atmospheric circulation of the entire Northern Hemisphere. This scenario has not yet been confirmed, but the indications have gained weight in recent days.

The polar vortex is a large mass of winds and very cold air that rotates around the North Pole, in the stratosphere, at an approximate altitude of between 15 and 50 kilometers. We could imagine it as a kind of giant whirlpool that keeps the coldest air concentrated in the polar regions.

During the autumn, this circulation gradually strengthens as we approach winter. Sometimes, however, large atmospheric waves can alter it, cause it to lose strength, displace it, or even split it into two parts. These alterations can be accompanied by a sudden stratospheric warming, which can lead to reversing the usual direction of the winds surrounding the vortex. All of this can favor the movement of cold air masses towards lower latitudes and modify the usual trajectory of storms.

What makes the current situation especially interesting is the calendar. Forecasts indicate that the weakening could culminate in mid-November. According to records available since 1959, and if the scenario proposed by the models is confirmed, we would be facing an extraordinarily early episode, several weeks earlier than what has been historically observed. All of this will have to be confirmed as we go along.

More rain and cold in Catalonia?

The big question is how all this could affect the weather in our home. And the answer is not as simple as thinking that a breaking of the polar vortex will automatically lead to a cold wave. If the disturbance ends up reaching the lower layers of the atmosphere, it could modify the position of the jet stream, which is the major current of winds that directs a good part of the storms and anticyclones. This could favor changes in the trajectories of Atlantic disturbances.

In the case of Catalonia, one of the scenarios that will need to be followed is a circulation more favorable to the arrival of fronts and storms, with more episodes of rain and snowfall in the Pyrenees. Regarding the cold, it could also increase the possibility of polar or continental air incursions at certain times. However, the most direct consequences of possible arctic air irruptions could be concentrated in the north and center of Europe. In Catalonia, a significant drop in temperatures or snow episodes at lower altitudes would depend on the specific position of the anticyclones, storms, and air masses.

When could we notice the effects?

If the polar vortex disruption is confirmed, its effects would not be immediate. The atmosphere needs time for the changes occurring at high altitude to be transmitted to the layers where the weather we notice on the surface is generated.

The first consequences could begin to manifest during the second half of November and at the beginning of December. Therefore, the upcoming model updates will be decisive. For now, it cannot be assured that Catalonia will have a start to winter that is colder or rainier than normal, but there are indications of an exceptionally early atmospheric disturbance that is worth following very closely.