Improvement of Nonconvective Aviation Turbulence Forecast in the World Area Forecast System (WAFS)

A global version of the Graphical Turbulence Guidance (G-GTG) turbulence forecasting system has been developed for the World Area Forecast System (WAFS). The G-GTG uses spatial gradients derived from an input global Numerical Weather Prediction model to infer hazard areas of aircraft-scale turbulence in the Upper Troposphere and Lower Stratosphere. The G-GTG provides an objective intensity (magnitude) of atmospheric turbulence directly affecting cruising aircraft as a function of the cube root of Energy Dissipation Rate (EDR; m^2/3s^-1), which is the standard for reporting aircraft turbulence by the International Civil Aviation Organization. The new version of the G-GTG provides both deterministic and probabilistic EDR forecasts that combine multiple diagnostics for Clear-Air Turbulence (CAT) and Mountain-Wave Turbulence. The G-GTG has been tested on both the NOAA’s Global Forecast System and the Met Office’s Unified Model outputs for 6-months (2016.10 – 2017.03). Statistical verifications of the G-GTG are examined using the Relative Operator Characteristic curves derived through comparisons to a global archive of in situ EDR data during the research period. It is found that both deterministic and probabilistic EDR forecasts from the new version of the G-GTG are superior to the current WAFS CAT forecast product, which is based on a single turbulence index for turbulence potential. This study suggests that the future version of the WAFS will provide calibrated turbulence severity, which will provide better turbulence guidance for strategic flight planning applications world-wide.