Making Flights Smoother, Safer, and Greener

By: Paul Williams

Atmospheric turbulence is the leading cause of weather-related injuries to air passengers and flight attendants. Bumpy air is estimated to cost the global aviation sector up to $1bn annually, and evidence suggests that climate change is causing turbulence to strengthen. For all these reasons, improving turbulence forecasts is essential for the continued comfort and safety of air travellers.

Clear-air turbulence is particularly hazardous to aviation because it is undetectable by on-board radar. A previously unrecognised mechanism that we proposed is now thought to be a significant source of clear-air turbulence. That mechanism is localised instabilities initiated by gravity waves that are spontaneously emitted by the atmosphere. Several years ago, we set out to use this knowledge to develop a practical turbulence-forecasting algorithm. Our method works by analysing the atmosphere and using a set of equations to identify the regions where the winds are becoming unbalanced, leading to the production of gravity waves and ultimately turbulence.

We conducted some initial tests on the accuracy of our forecasting algorithm, with promising results. At that time, the US Federal Government’s goals for aviation turbulence forecasting were not being achieved, either by automated systems or by experienced human forecasters, but our algorithm came tantalisingly close. We published our results, concluding that major improvements in clear-air turbulence forecasting could result if our method were to become operational.

Rough air has long plagued the global aviation sector. Tens of thousands of aircraft annually encounter turbulence strong enough to throw unsecured objects and people around inside the cabin. On scheduled commercial flights involving large airliners, official statistics indicate that several hundred passengers and flight attendants are injured every year, but because of under-reporting we know that the real injury rate is probably in the thousands.

Turbulence also has consequences for the environment, by causing excessive fuel consumption and CO2 emissions. Up to two-thirds of flights deviate from the most fuel-efficient altitude because of turbulence. This wastes fuel and it contributes to climate change through unnecessary CO2 emissions. At a time when we are all concerned about aviation’s carbon footprint, reducing turbulence encounters represents an attractive opportunity to help make flying greener.

Furthermore, climate change is expected to make turbulence much worse in future. In particular, our published projections indicate that there will be hundreds of per cent more turbulence globally by 2050–2080. These findings underline the increasingly urgent need to develop better aviation turbulence-forecasting techniques.

It is therefore excellent news for air travellers that our improved turbulence-forecasting algorithm is now being used operationally by the Aviation Weather Center (AWC) in the National Weather Service (NWS), which is the US equivalent of the Met Office. The turbulence forecasts are freely available via an official US government website. They forecast turbulence up to 18 hours ahead, updated hourly. Our algorithm is the latest in a basket of diagnostics that are optimally combined to produce the final published forecast.

Every day since 20 October 2015, turbulence forecasts made with our algorithm have been used in flight planning by commercial and private pilots, flight dispatchers, and air-traffic controllers. They are benefiting from advance knowledge of the locations of turbulence, with greater accuracy than ever before, allowing flight routes through smooth air to be planned. Pilots and air-traffic controllers are benefiting from a reduced workload, because unexpected turbulence results in burdensome re-routing requests. Airlines are benefiting from fewer unplanned diversions around turbulence and reduced fuel costs and emissions associated with those diversions.

To date, our algorithm has helped improve the comfort and safety of air travel on billions of passenger journeys. Our algorithm has won several awards recently, but the real prize is the knowledge that it is making a difference to people’s lives every day. In the time it has taken you to read this article, thousands of passengers have taken to the skies and are benefiting from smoother, safer, and greener flights.


Williams, P. D. and Storer, L. N. (2022) Can a climate model successfully diagnose clear-air turbulence and its response to climate change? Quarterly Journal of the Royal Meteorological Society148(744), pp 1424-1438. doi:10.1002/qj.4270

REF (2021) Improved turbulence forecasts for the aviation sector, Research Excellence Framework (REF) Impact Case Study, on-line at

Lee, S. H., Williams, P. D. and Frame, T. H. A. (2019) Increased shear in the North Atlantic upper-level jet stream over the past four decades. Nature572(7771), pp 639-642. doi:10.1038/s41586-019-1465-z

Williams, P. D. (2017) Increased light, moderate, and severe clear-air turbulence in response to climate change. Advances in Atmospheric Sciences34(5), pp 576-586. doi:10.1007/s00376-017-6268-2

McCann, D. W., Knox, J. A. and Williams, P. D. (2012) An improvement in clear-air turbulence forecasting based on spontaneous imbalance theory: the ULTURB algorithm. Meteorological Applications, 19(1), pp 71-78. doi:10.1002/met.260

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