The UK's autumn temperatures started higher than average, but temperatures are expected to fall to seasonal average levels or below during the week.
Alongside this change, reports have emerged that the “polar vortex” could bring severe cold.
However, the possibility of a weakening polar vortex and an actual cold wave are not the same thing, and winter weather cannot be determined by El Niño alone.
3-line summary
1. The polar vortex is a band of winds that traps cold air in the Arctic
2. If it weakens, cold air can spread southward
3. An increased possibility is not the same as a confirmed cold wave
Strong westerly winds that hold Arctic cold air in place
The polar vortex refers to a band of strong westerly winds circulating around the Arctic. The London Evening Standard explained that this band of winds helps trap extremely cold air in the Arctic. If the band weakens or becomes disrupted, the flow can bend, allowing cold air to move south toward North America and Europe.
Based on this explanation alone, it may sound as though the polar vortex necessarily means heavy snow or extreme cold. However, the key point made in the article is that the possibility of cold air moving southward may increase. Where, when, and how severe the cold will be cannot be determined by this definition alone.
The UK Met Office stated that if the stratospheric polar vortex weakens, the possibility of a sudden stratospheric warming (SSW) event increases, and as a result, the possibility of cold weather may also rise. SSW was introduced as a phenomenon in which air at an altitude of 10~50km above the ground warms.
Even with El Niño, the winter forecast cannot be stated with certainty
According to reports, El Niño, a natural phenomenon that occurs in the tropical Pacific, may be associated with a weakening polar vortex in late winter. Research by the Chemical Sciences Laboratory of NOAA, an agency of the US government, concluded that El Niño tends to promote the breakdown of the polar vortex, particularly in late winter.
However, the UK Met Office drew a distinction, saying that El Niño is only one of several factors influencing the UK's weather. As El Niño strengthens, the possibility of wetter and stormier-than-average weather in late autumn and early winter may increase, while the possibility of milder-than-average conditions was also mentioned. The potential for cold weather may rise in the latter part of winter, but the explanation noted that the exact weather pattern could also lead to a different outcome.
The wording used by a UK Met Office official, as reported by LBC, described a subtle change in probability, not “certainty.” This means that even if a strong El Niño is observed, it alone does not determine whether extreme cold will occur. The point to note in this forecast is that, rather than predicting severe cold based on the name “polar vortex,” the seasonal forecast explained that the possibilities of wet weather, storms, flooding, and cold would each increase.
What appears first is a temperature drop and rain
The BBC forecast that temperatures across the UK would fall over the course of the week, with Wednesday’s daytime highs reaching about 11 degrees in northern Scotland and 17 degrees in southern England. This represents a major change compared with the previous week, when temperatures reached as high as 28 degrees in some areas.
The band of rain clouds is expected to move south between Monday and Wednesday. More rain is expected in the north and west, while heavy rain accompanied by thunder and lightning may occur in southeast England. After the rain passes, cooler air will remain, and light frost may be possible in places where frost is likely to form.
The drop in temperatures during early autumn, after a warmer-than-average start to the season, is a forecast concerning short-term weather changes. By contrast, the polar vortex and El Niño concern the possibility of climate conditions that may continue into the latter part of winter. Rather than combining the two into a single statement that “record-breaking cold is coming soon,” it is more accurate to distinguish between short-term temperature changes and long-term probability forecasts.
References
Tags #polarvortex #polarvortex #ElNiño #UKweather #coldwave #winterweather #suddenstratosphericwarming #SSW #MetOffice #heavysnow #temperaturedrop #climatephenomenon