Update on the Graphical Turbulence Guidance Nowcast (GTGN)

Commercial and general aviation aircraft frequently encounter unexpected atmospheric turbulence. Though rarely fatal, these encounters often result in serious injuries to aircraft occupants or rerouting of flights. According to the Federal Aviation Administration (FAA), turbulence is the leading cause of injuries to passengers and flight attendants in non-fatal accidents. Approximately 58 passengers in the United States are injured by turbulence each year. According to the NTSB, during the years 2000 thru 2016, U.S. air carriers had 217 weather-related accidents, of which 75% were caused by turbulence. In addition, estimates put the cost to air carriers of these injuries (medical attention and lawsuits), equipment damage and maintenance/inspection, and rerouting at $100 million per year.

In the 1990’s, the FAA’s Aviation Weather Research Program began funding research efforts at the National Center for Atmospheric Research (NCAR) to improve turbulence forecasting and reporting capabilities. NCAR developed the Graphical Turbulence Guidance (GTG) product, which provides gridded forecasts of turbulence intensity for use in strategic flight planning by air crews and weather forecasters supporting aviation. GTG provides forecasts for turbulence expressed in the objective metric Eddy Dissipation Rate (EDR), which is the International Civil Aviation Organization’s standing reporting metric for turbulence. The current generation of GTG provides turbulence forecasts for all flight levels surface to 45,000 feet, valid in hourly increments out to 18 hours. GTG also provides explicit forecasts for clear air turbulence and mountain-wave induced turbulence.

While GTG is an excellent tool for strategic flight planning, it fails to provide short-range representations of the current turbulent state of the atmosphere that benefit tactical flight decision-making by air crews, dispatchers, and air traffic controllers. To this end, under FAA funding, NCAR has developed the GTG-Nowcast (GTGN) product, which provides a rapidly updated (every 15 minutes, valid for the next 15 minutes) turbulence “nowcast”. GTGN uses the GTG forecast as a starting point, then “nudges” it with the most recent turbulence observations available, such as pilot reports, automated EDR turbulence measurements from aircraft, and NEXRAD radar measurements of turbulence in cloud. The result is a more accurate depiction of short-term turbulence for use in real-time routing decisions.

Independent evaluations show that GTGN is an improvement over the GTG product and should be moved into operational use within the airline industry. As a result, an FAA Safety Risk Management Panel was convened in July 2019 that unanimously voted to allow the product to be disseminated to industry.

This presentation will examine the technical and quality assessments of GTGN, present the results of the user evaluations, and summarize the current state of availability of the product for industry stakeholders.