A major Sudden Stratospheric Warming (SSW) event is predicted to occur as we start the new year. If the models are correct, we can expect prolonged extremely cold temperatures to affect parts of the northern hemisphere by mid-January.
SSW refers to a rapid rise in temperatures between 10 and 50 km (6.2 - 31 miles) above the surface of our planet.
Several weeks later, we see knock-on effects on the jet stream, which can significantly affect weather in the troposphere -- bringing prolonged extremely cold temperatures such as witnessed in 2018 with an extreme event dubbed 'Beast from the East.'
"The stratospheric sudden warming can sometimes cause the jet stream to ‘snake’ more, and this tends to create a large area of blocking high pressure," the UK Met Office meteorologists explained.
"Typically, this will form over the North Atlantic and Scandinavia."
"This means that northern Europe, including the UK, is likely to get a long spell of dry, cold weather, whereas southern Europe will tend to be more mild, wet and windy. On the boundary of these areas, cold easterly winds develop and in some cases the drop in temperatures leads to snow, which is what happened in early 2018."
Stratospheric warming events in winter, are very important, as they can change the course of winter weather development and affect global circulation, Adrej Flis of the Severe Weather Europe said.
"We need to see how exactly the SSW event will play out before we can simulate proper weather results," Flis added.
"But, a collapsed vortex always greatly increases the chances for winter weather towards Europe and the Continental United States. A lot depends on how the existing pressure pattern looks, while the effects from the stratosphere come crashing down from above.
"In some cases, the effects can be partially “deflected” and we don’t feel much of a change in our daily weather. But in most cases, the effects can have a major influence on the distribution of weather systems across the hemisphere."
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