From one extreme to another, the temperatures across Europe have been on a rollercoaster journey this winter.
Greece or Spain have experienced some of the heaviest snowfall in several decades, temperatures have been exceptionally mild for the season in western Europe and there’s been freezing cold in the east.
So, why has there been such extremes in the weather?
The answer lies within the variability of large scale weather pattern drivers: the polar vortex and the jet stream.
The jet stream — currents of fast-flowing, meandering air high above the Earth — has displayed interesting behaviour over the last few weeks following a sudden stratospheric warming.
This led to a weak polar vortex — areas of low pressure and cold air surrounding the Earth’s north and south poles — and in turn disrupted the jet stream; throwing a typical weather pattern out of the window.
This allowed extreme cold air to pour out of the Arctic and into mid-latitude continental regions like Europe, North America and Asia. There has also been record-breaking warmth across the Northern Hemisphere, this opposite extreme often goes hand-in-hand when the jet stream becomes weak and wavy.
Below is a snapshot of the weather setup across Europe in mid-February 2021.
While Spain, Portugal and parts of France basked in spring warmth, eastern Europe shivered in extreme cold with snow reported as far south as Athens and then eventually parts of north Africa and Saudi Arabia.
Wild meanders in the jet stream account for the strong temperature contrasts. The wavy jet stream allows warmth to push north in some places while cold air leaks south from Polar regions in others. It is useful to compare the track of the jet stream to the airmass temperature to show how they are connected.