Met Office & Sudden Stratospheric Warming
By Paul Homewood
The Met Office has an interesting post on sudden stratospheric warming, sometimes referred to as the polar vortex:
Our atmospheric scientists are predicting a dramatic change in high altitude winds 50km above the ground and the imminent occurrence of an event known as a sudden stratospheric warming (SSW) in early March.
Professor Adam Scaife, Head of Monthly to Decadal Prediction explains: “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.”
The phenomenon begins with a wave-like disturbance which travels up into the high-altitude jet stream. Scaife said: “This disturbance can grow to a point where it turns over and breaks, just like a wave on a beach.”
Normally the jet stream flows from west to east with some north and south oscillation, but the force from this high altitude disturbance pushes against the jet stream until the winds actually reverse and flow from east to west instead. Air then falls into the Arctic and is compressed so that it starts to warm: the temperature can rise by as much as 50C in just a few days.
Professor Scaife added: “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.”
Sudden stratospheric warming events occur on average every couple of years and our long-range forecasts have consistently suggested an increased risk of sudden stratospheric warming towards the end of this winter. The last big event was in early 2013 and was followed by a cold end to winter. Although the impact of the current event is unlikely to be as severe, it increases the risk of cold north easterlies and wintry weather for the UK over the next few weeks.
Does this mean we’ll see snow at Easter?
You may have seen in the media that we will see snow at Easter. At this stage it is too early to provide details about what the weather will bring for Easter. Beyond a week ahead we can’t say what will happen on specific days, but we can give an idea of what type of weather we can expect.
As always we are working with our customers such as EasyJet and other major airlines, airports such as Heathrow and Gatwick, local councils, and energy providers, together with government partners in Highways England and Transport Scotland to ensure they are prepared for the current wintry conditions and whatever the weather may bring in the coming weeks.