The sting jet sits on the south side of the hooked area of cloud, resembling a scorpion’s tail, which wraps around a low pressure centre.
On 27th and 28th October 2013 severe storm St Jude hit north-western Europe causing at least 17 deaths. It has been mentioned in media that there was probably phenomenon called ‘sting jet’ associated with St Jude. But what is a ‘sting jet’?
St Jude storm is often compared with the well remembered destructive 1987 Great Storm, which was the first storm where a sting jet was identified. A sting jet is a flow of air that originates in the cloud head (see picture) associated with a rapidly deepening area of low pressure, with pressure falls of more than 24hPa in 24 hours. It develops on the south side of the hooked tail of cloud some 5km above the ground. Air rushes downward from a warm front to a cold front. The sting jet can take around 3 to 4 hours to descend towards ground level and, as it does so, it passes through layers of ice crystals that evaporate. This evaporative cooling causes the sting jet to accelerate to high speeds of more than 100mph.
One of the biggest challenges for forecasters is predicting where and when sting jets will hit. In a new study published in the journal Weather and Forecasting, researchers discovered the winds strike where the storm's temperature gradient, or difference in temperature between two locations, is weakest.
David Schultz, lead study author and a professor at the University of Manchester said ‘The irony is that the winds are strongest in the cyclone where the front is weakening most intensely. Our findings are significant because they tell us exactly where we can expect these winds and give forecasters added knowledge about the physical processes that are going on to create this region of strong winds.’
Sting jets only arise in a certain type of storm, called Shapiro-Keyser cyclones. These have a ‘T-bone’ structure that keeps the warm and cold fronts within the storm from meeting, and a hooked tail of cloud associated with a back-bent front that is just the right shape for triggering sting jets. Research led by Oscar Martínez-Alvarado from the University of Reading found that thirty two out of a hundred intense North- Atlantic storms in the past two decades fulfilled the conditions for a sting jet event. The study also found that multiple sting jet occurrences within one storm were not uncommon and that all of the storms with an existing sting jet precursor originated south of 50°N.
Other existing and well documented cases of sting jet storms in the North Atlantic occurred on 26th February 2002 (called storm Anna); 27th October 2002 (called storm Jeanette); 8th January 2005 (called storm Gudrun) and 8th December 2011 (called storm Friedhelm). If you are wondering where the storm names come from - since 1954, the Institute of Meteorology of the Free University of Berlin has been naming ‘highs’ and ‘lows’ which influence the weather in middle Europe. Those names are used by some national meteorological services as part of weather briefings in newspapers, on radio and television. The scheme is called ‘Adopt-a-Vortex’ and allows anybody to participate in the naming process. To find out more click here.