The Polar Vortex is in the news again, with rarely-seen heavy snowfall across central Texas and western Louisiana, and record-breaking snowfall in Madrid, Spain (as much as 20”/50 cm in some areas). How are these extreme weather events related, when they occurred an ocean apart?
Though it seems like a new “hot” topic in weather, the Polar Vortex, or PV, is not new at all — it’s likely been around for as long as humans have been recording the weather.
Put simply, the PV are wide expanses of swirling cold air that are parked in polar regions, meaning there’s one located in the southern hemisphere as well. A vortex consists of a large-scale, upper-level, low pressure center that is semi-permanent and rotates fairly tightly around the Earth’s poles.
At its core, the PV represents the coldest part of winter for the Northern Hemisphere. Canada and northern Asia experience the lion’s share of the cold, but when the PV moves, it takes its cold air with it.
The strength of the PV relies on the temperature difference between the Earth’s poles and the Equator: i.e. the colder the poles, the stronger the PV. So, although the PV is technically happening year-round, it’s during these winter months that the vortex is at its strongest (and coldest). When a PV is strong and stable the cold air is “locked” near the North Pole leading to milder winters across the Northern Hemisphere.
In early January 2021, a phenomenon known as a Sudden Stratospheric Warming (SSW) took place. The origin of SSW is largely a mystery, but they are more likely to occur when stratospheric winds reverse direction while the Earth is experiencing a low period of the solar cycle. During SSW events, temperatures near the pole dramatically increase (although the temperatures still stay well below freezing), which causes the PV to weaken and split into smaller pieces.
As PV weakens, the polar storm track shifts south and allows colder air and unsettled weather to penetrate into the lower latitudes. When the right placement of colder air and the storm track line up you can get unusual winter weather events such as the recent ones we saw in Texas, Louisiana and Spain last week.
Yes — the sudden stratospheric warming event that initially split the PV will eventually dissipate as the warm stratospheric winds retreat to their more typical altitudes. The absence of the SSW allows the PV to coalesce and return to its traditional location with its primary characteristics.
According to Fred Schmude, Senior Long-range Scientist, StormGeo, the current SSW event could last through the latter half of January and possibly into early February, leading the southern and eastern U.S. to potentially see another round of wintry weather. It does appear the effects of the SSW will weaken during early to mid-February allowing for a milder weather trend over the eastern half of the U.S.
For Europe and the Nordics, Beathe Tveita, Forecaster, StormGeo explains that the PV is positioned above Scandinavia and expected to move over Siberia and south of Greenland, which will continue to steer low pressure into Central Europe. This means very wet conditions over the Continent and more changeable temperatures depending on air moving in from the Atlantic and north-northeasterly colder air.