A historical weakening of the polar vortex has been detected in the upper atmosphere, according to the Finnish Meteorological Institute (FMI). The event, first observed in early November, is the earliest such disturbance on record since the institute’s database began in 1958. Henri Nyman, FMI’s senior meteorologist, explained that the vortex, which normally strengthens and weakens annually as part of the seasonal cycle, is currently in a state of disruption. “The disturbance is already underway, but its effects will not be visible in Finnish weather until it propagates from the stratosphere down into the troposphere,” Nyman said. He added that the weakening could reach the troposphere by the end of November, potentially influencing weather in Finland. The polar vortex is a high‑altitude, low‑temperature circulation that drives the prevailing westerly winds in the upper atmosphere. When the vortex weakens, the westerly flow can diminish, allowing cold air masses from the polar region to move further south. However, Nyman cautioned that this does not automatically mean colder weather in Finland. “The ultimate weather outcome depends on the placement of high and low pressure systems,” he said. He noted that if the cold air remains over Greenland, Finland may experience cooler temperatures, whereas if it shifts toward Russia, parts of Finland could remain warm. Despite the early weakening, current forecasts for Finland indicate a continuation of relatively mild autumn weather. Nyman suggested that the El Niño phenomenon, which is presently strengthening the westerly flow over the North Atlantic, may be contributing to the mild conditions. “In El Niño years, the early winter in Northern Europe tends to be milder, while the late winter is often colder,” he said. The interaction between the El Niño effect and the polar vortex disturbance could delay the full impact of the vortex weakening. Nyman acknowledged that many variables remain uncertain. “There are still many open questions about how the rest of the winter will unfold,” he said. He projected that a colder spell could emerge in late November or early December, but the duration and intensity would depend on a range of atmospheric factors that are difficult to predict at this stage.