Long read
Extratropical cyclones – forecasting the sting in the tail
Published
11 Mar 2024
Authors
Marc Skinner – Marine forecaster
Neville Smith – Global lead - weather forecasting
First identified 20 years ago, this fast-moving and often devastating weather phenomenon has proved devilishly tricky to predict. However, some high-resolution forecasting models can now provide a welcome beacon of light in the storm.
The starting point for a sting jet is an extratropical cyclone, a large-scale, low-pressure storm system that can last for several days and sometimes more than a week. These cyclones typically form in the middle latitudes, between 30° and 60° from the Equator, and play a significant role in driving much of Earth’s weather.
What is a sting jet?
A sting jet is a core of extremely strong winds that occurs within an extratropical cyclone and extends towards the ground. Although it can cause severe damage at the Earth’s surface, it affects a much smaller area than the main storm – typically around 100 km in the maximum width. Additionally, it has a far shorter duration, usually three to four hours.
Most extratropical cyclones don’t have a sting jet. For example, it’s estimated that they occur in around 39-49% of the strongest extratropical cyclones over the North Atlantic.
What causes sting jets to form?
Sting jets tend to occur in a particular type of extratropical cyclone known as a Shapiro-Keyser cyclone. This type of weather system features low pressure at its centre and forms outside the tropics, causing various weather events such as rain and storms.
On a surface pressure chart, sting jets have a distinct appearance that differs significantly from a typical low-pressure system. These lows develop much more rapidly through a process known as explosive cyclogenesis, during which the associated warm and cold fronts do not merge to form an occlusion. The point at which the cold and warm fronts fail to ‘attach’ is known as the frontal fracture region.
Like all extratropical cyclones, the Shapiro-Keyser cyclone has two conveyor belts: warm and cold. The warm conveyor belt moves parallel to the surface cold front, rising above the surface warn front. As it rises, the moisture it carries condenses, resulting in a cloud head. The cold conveyor belt runs parallel to the surface warm front, then wraps around behind the surface cold front.
The sting jet forms inside the cloud head, in the mid-levels of the troposphere. which is the lowest layer of the Earth’s atmosphere, around three to four kilometres above the ground. Evaporative cooling then causes the jet to accelerate downwards towards the frontal fracture zone and surface. As the jet descends, snow and rain fall into it (the snow turns into rain). The rain evaporates, and the jet becomes colder and denser, causing it to sink to the surface. When the jet hits the surface ahead of the cold conveyor belt, it generates winds that are far stronger than those normally associated with an extratropical cyclone. The wind speed depends on the stability of the atmosphere.
Additional mechanisms may also be involved in generating a sting jet, such as weakened weather fronts and some types of convective instability – the relative importance of these processes remains an active area of research. It’s a complex topic, not least because an extratropical cyclone can produce several sting jets – and a sting jet can create damaging winds in many areas.
3D idealised image of a Shapiro-Keyser Cyclone
Forecasting sting jets
Understanding sting jets is crucial for offshore operations. They are associated with intense and localised weather phenomena, including sudden and extreme wind events. These events can pose significant risks to offshore operations, affecting the safety of personnel, maritime assets, and infrastructure. The high winds associated with sting jets can lead to dangerous sea conditions, impacting vessel stability and navigation. Additionally, strong winds can pose challenges to helicopter operations, often used for personnel transfer to offshore infrastructure. For industries such as offshore wind, the structural integrity of offshore installations may be compromised by the intense winds associated with sting jets. Therefore, a comprehensive understanding of sting jets is essential for companies to implement effective safety measures, optimise operational planning, and mitigate potential risks to personnel and assets operating in offshore environments.
Forecasting the sting jet phenomenon, however, can be very challenging for forecasters. One reason for this is that extratropical cyclones are rather like snowflakes: each one forms under its own specific conditions, which may or may not combine to make a sting jet. Another factor is that forecast models with a finite resolution often struggle to predict sting jets accurately because of their small size.
However, rapid advances in technology continue to improve the accuracy of sting jet forecasting. Some higher-resolution models can now detect small areas of very strong winds within an extratropical cyclone, indicative of a sting jet. It’s also now possible to spot sting jets on satellite imagery – a hook-shaped cloud swirling around the low centre with a sharp point (the ‘sting’) at the end of its tail.
At Fugro, when producing forecasts for our clients, if there’s potential for a sting jet to form, we usually increase the winds above model output and reflect the increased uncertainty regarding the peak wind speed in the confidence section of our report.
Satellite imagery indicating a potential sting jet
To conclude
The understanding and forecasting of sting jets are paramount for the safety and efficiency of offshore operations. These intense and localised weather phenomena pose significant risks to personnel, maritime assets, and infrastructure. While the complexity of extratropical cyclones presents challenges for accurate prediction, advancements in technology are steadily improving forecasting capabilities. By leveraging higher-resolution models and satellite imagery, forecasters can better identify the formation of sting jets and provide timely warnings to mitigate potential hazards. As industries continue to operate in offshore environments, maintaining a comprehensive understanding of sting jets remains essential for implementing effective safety measures and optimising operational planning. Through ongoing research and collaboration, we can enhance our ability to anticipate and respond to the impacts of sting jets, ensuring the safety and resilience of offshore operations in the face of extreme weather events.
FAQs
What is a sting jet and how do sting jets form?
A sting jet is a meteorological phenomenon characterised by a concentrated core of very strong winds that can cause significant damage over a relatively small area. The term sting jet originates from the hook-shaped cloud that appears on satellite imagery, resembling the scorpion’s tail of a cyclone.
Sting jets typically form within certain intense extratropical cyclones, most often in the North Atlantic, and are considered among the most damaging extratropical cyclones.
Sting jet formation begins in an individual low pressure system, usually a Shapiro-Keyser cyclone, where the cyclone’s warm and cold conveyor belts interact. Moist air in the warm conveyor belt rises above the bent-back warm front, creating a mid-tropospheric cloud head with light and dark shades that can be traced on satellite images.
Meanwhile, air parcels from the cold conveyor belt wrap around the cyclone centre, cooling as they descend. Evaporative cooling of this descending air, combined with air stretching and cooled air sinking from the cloud head, accelerates the flow toward the frontal fracture region.
As the sting jet develops, very strong winds descend from the mid tropospheric cloud head in a few hours, producing intense winds at the surface.
These winds can be far stronger than the surrounding cyclone and generate damaging winds that affect offshore operations and land areas such as Southern England and Western Europe. Dark fingers of dry air and water droplets in the cloud head, along with the bent back warm front, serve as precursors visible in satellite imagery, helping meteorologists identify potential sting jet evolution.
In summary, sting jets form through the interaction of warm and cold conveyor belts, evaporative cooling, and descending cooled air from the cloud head, creating a meteorological phenomenon capable of producing very intense winds and high wind speeds over a short period.
How can sting jets impact offshore operations?
Sting jets can have a major impact on offshore operations due to the very strong winds they produce in a matter of hours. As a sting jet develops within intense cyclones, often in the North Atlantic or along storm tracks affecting Western Europe, air from the cold conveyor and warm conveyor belts descends rapidly from the mid-tropospheric cloud head, carrying dry air, water vapour, and strong winds that can compromise vessel stability, offshore platforms, and helicopter transfers.
Satellite images often reveal sting jet precursors, such as the hook-shaped scorpion’s tail and darker shades in the cloud head, allowing forecasters to anticipate where these high winds may descend.
Fugro supports offshore operators by combining high-resolution weather models with observational data to monitor low pressure systems, track sting jets, and assess potential risks. This enables companies to implement safety measures, optimise operational planning, and minimise the chance of damage caused by the intense winds associated with the term sting jet.
Are sting jets common in all extratropical cyclones?
Sting jets are not common in all extratropical cyclones. They typically develop only in certain intense low pressure systems where the interaction of cold air from the cold conveyor and warm air from the warm core creates conditions that can produce sting jets.
Observations from satellite images, including darker the shade of cloud heads and patterns of water vapour, help meteorologists identify potential sting jet precursors. While more frequently observed in the Eastern North Atlantic and Northern Hemisphere, particularly during great storms, they remain relatively rare events across the Southern Hemisphere and North Pacific.
Even in strong extratropical cyclones, most systems do not generate the concentrated core of very strong winds characteristic of the term sting jet, highlighting the importance of targeted forecasting and monitoring.
What role did sting jets play during Storm Eunice?
During Storm Eunice, sting jets produced very strong winds that caused significant damage across parts of Western Europe, particularly in the Northern Hemisphere. Fugro’s analysis of weather models and satellite imagery highlighted how the descending air from the cloud head and cold conveyor intensified surface wind speeds, helping offshore operators and infrastructure planners anticipate and mitigate risks.
How do meteorologists forecast sting jets accurately?
Meteorologists forecast sting jets accurately by closely monitoring the evolution of intense extratropical cyclones in the North Atlantic and other storm tracks. High-resolution weather models simulate the behaviour of individual low pressure systems, tracking the interaction between the warm and cold conveyor belts and the movement of air parcels within the cyclone centre.
Observing the cloud head, including light and dark shades, dark fingers of dry air, and the hook-shaped cloud often described as the scorpion’s tail, allows forecasters to identify sting jet precursors and anticipate where very intense winds may descend.
Satellite images play a crucial role in detecting air stretching, cooled air, and water droplets in the mid tropospheric cloud head, giving clues to potential sting jet formation. By combining model output with real-time satellite imagery, meteorologists can estimate the likely wind speeds and timing of damaging winds in areas such as Southern England and Western Europe. Even though sting jets develop in just a few hours, understanding the dynamics of the cold conveyor belt jet, evaporative cooling, and the bent-back warm front enables forecasters to generate sting jets warnings and provide guidance to mitigate significant damage.
What are the main signs that a sting jet may develop within a cyclone?
The main signs that a sting jet may develop within a cyclone are closely linked to the dynamics of cold and warm air within an intense low pressure system.
As the cold conveyor and warm core interact, meteorologists look for patterns in the cloud head, including darker the shade and areas of concentrated water vapour, which can indicate air descending rapidly to produce sting jets. Observations from the Northern Hemisphere, particularly during great storms, show these precursors most clearly, though similar signs can appear in the Southern Hemisphere.
By monitoring these indicators, forecasters can anticipate the formation of very strong winds associated with sting jets and provide early warnings to mitigate potential impacts.
How do sting jets compare to other extreme weather events?
Sting jets differ from many other extreme weather events because they develop rapidly, often in just a few hours, and produce highly localised zones of very strong winds. Their formation, driven by the interaction of cold air and warm air within an intense low pressure system, can concentrate water vapour in descending air, making them particularly hazardous; research from the Royal Meteorological Society shows that while most are observed in the Northern Hemisphere, similar dynamics can occasionally occur in the Southern Hemisphere.
Can offshore infrastructure withstand the winds generated by a sting jet?
Offshore infrastructure can be at significant risk from the damaging winds produced by a sting jet, particularly during intense cyclones in the North Atlantic and along key storm tracks affecting Western Europe. As sting jets develop, very strong winds descend from the mid-tropospheric cloud head, where light and dark shades, dark fingers of dry air, and the hook-shaped scorpion’s tail often appear in satellite images as precursors. These winds can reach extremely high wind speeds in mere few hours, challenging the structural integrity of offshore platforms, turbines, and vessels.
Fugro’s services help operators assess and mitigate these risks by combining high-resolution weather models with observational data, including satellite images, to understand the evolution of individual low pressure systems and the dynamics of the cold and warm conveyor belts.
By mapping areas where sting jets may descend and produce intense winds, Fugro supports informed operational planning, enabling companies to reinforce structures, optimise safety procedures, and minimise the potential for significant damage from this meteorological phenomenon.
How can improved forecasting reduce risks from sudden weather events?
Improved forecasting reduces risks from sudden weather events by providing early warnings of strong winds, intense cyclones, and sting jets before they impact offshore operations.
By monitoring low pressure systems and the interaction of cold and warm air in the North Atlantic, Eastern North Atlantic, and other storm tracks, meteorologists can track how sting jets descend from the mid-tropospheric cloud head, where features like the scorpion’s tail, darker the shade in satellite images, air stretching, and dry air act as precursors. Understanding the evolution of the cold conveyor and warm core within these systems allows forecasters to anticipate the production of very strong winds and mitigate potential damage.
Fugro leverages high-resolution weather models, satellite imagery, and observational data to provide clients with actionable insights, enabling safer operational planning and proactive measures to reduce the impacts of sudden weather events in the Northern Hemisphere, Southern Hemisphere, and other high-risk regions such as the North Pacific.
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