True or false? During the winter in the northern hemisphere there is a large mass of cold air in the upper atmosphere, also known as the stratosphere. This vortex is what causes air to move from west to east usually. However, in February 2018 there was a considerable rise in air temperature of around 50°C 18 miles above the Earth at the North Pole. Sudden stratospheric warming caused a weakening of the jet stream leading to a change in the direction of the winds approaching the UK from west to east to east to west, allowing a cold air mass (polar continental air mass) from Russia to cover The UK.