Description

The Graphical Turbulence Guidance (GTG) system is a set of aviation weather tools used to forecast atmospheric turbulence for flight planning and safety. It combines various numerical weather prediction models to create 3D, high resolution maps of potential turbulence.

GTG is derived from airborne turbulence observations and U.S. National Weather Service (NWS) model data. GTG computes the results from multiple turbulence algorithms, then compares the results of each algorithm with turbulence observations from PIREPs, AMDAR data, and EDR reports to determine how well each algorithm matches reported turbulence conditions from these sources. GTG then weighs the results of this comparison to produce a single turbulence forecast expressed as Eddy Dissipation Rate (EDR). The success of GTG is proportional to the number of in situ reports available to verify the algorithms. This means that the accuracy of GTG improves during daylight hours when there is more traffic.

GTG Global (GTGG)

The current operational version of GTG for global long-range hourly forecasting is GTGG. It is based on 13 km Global Forecast System (GFS) and UKMET models.

Coverage is from 100ft AMSL up to FL500, producing hourly forecasts for the first 6 hours, then 3-hourly forecast up to 48 hours, updating every 6 hours. GTGG focuses on a combined deterministic forecast of Clear Air Turbulence (CAT) and Mountain Wave Turbulence (MWT). The output is based on the EDR, which provides a standardised, objective measurement of turbulence intensity independent of aircraft type.

The Graphical Turbulence Guidance Nowcast (GTGN) 

GTGN is a tactical aid for aviation providing a nowcast of the current turbulence state of the atmosphere in near real time. Currently this service only covers the Continental United States.

Further Reading

• Further information on the FAA Turbulence Program