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Sudden stratospheric warming to bring a snap of cold weather over UK


Meteorologists from the UK Met Office have predicted a sudden stratospheric warming (SSW) will occur in early March 2016. The phenomena could affect the surface weather, increasing the risk of prolonged wintry conditions over parts of northern Europe and the UK.

The sudden stratospheric warming (SSW) phenomenon is a rapid warming episode which takes place between 10 and 50 km (6.2 and 31 miles) of the Earth's atmosphere. During the warming, temperatures can climb for up to 50 °C in only a few days time. 

SSW begins with a wave-like disturbance which travels into the high-altitude jet stream system, and can grow to a point to breaking, exhibiting similar behavior like the breaking beach waves. The jet stream usually flows in the west-to-east direction with some north and south oscillation. The disturbance can cause the winds to turn in the opposite direction. When that happens, the air falls into the Arctic and gets compressed, causing the rapid warming.

“Sudden stratospheric warming events occur high up in the atmosphere and involve a complete reversal of the high-altitude polar jet stream – they can even affect weather at the surface, and for the UK, a sudden stratospheric warming increases the risk of wintry weather,” Professor Adam Scaife, Head of Monthly to Decadal Prediction explained.

YouTube video

Video credit: Met Office

“This reversal of high altitude winds can also burrow down into the lower stratosphere. Once it is within reach of weather systems in the lower atmosphere the Atlantic jet stream often weakens and moves south. This allows cold air from the east into northern Europe and the UK.”

Such stratospheric warming last time occurred in early 2013 when the winter had a strong and cold ending. SSW occurs every few years, although the impact of the current event should not be so dramatic.

Under normal weather conditions, the UK region is under the influence of a mild Atlantic air inflow. However, an SSW episode causes the low pressure areas to weaken and the prevailing jet stream shifts south which causes the high-pressure area over the North Atlantic to block the mild air flow, and drags in the cold continental air to the east. Stratosphere warming doesn't always produce such synoptical situations, however, a cold snap does occur quite frequently, which means the outbreak increases a risk of cold north easterlies and wintry weather over UK in the coming weeks.

Featured image credit: UK Met Office

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