Inter-comparison of Upper-Level Turbulence Forecasts using Graphical Turbulence Guidance (GTG) on GFS and UM models

In order to mitigate unexpected extra costs due to turbulence encounters, the Graphical Turbulence Guidance (GTG; Sharman et al. 2006) system has been developed to diagnose potential areas of clear-air turbulence (CAT) and mountain wave-induced turbulence (MWT) especially at cruising altitudes in upper troposphere and lower stratosphere (UTLS). In this GTG system, multiple CAT and MWT diagnostics are optimally combined to produce forecast turbulence in terms of Eddy Dissipation Rate (EDR), which is a standard measure of atmospheric turbulence by the International Civil Aviation Organization (ICAO). GTG is currently operational for domestic Contiguous United States (CONUS) domain (i.e., CONUS GTG), which will be useful for international operations. Two World Area Forecast Centers (WAFCs) in Washington, US and in London, UK have been testing to implement the GTG system on their global Numerical Weather Prediction (NWP) models like NOAA’s Global Forecast System (GFS) and Met Office’s Unified Model (UM). In this study, EDR forecasts generated from GFS and UM are compared and evaluated using observed Pilot reports (PIREPs) for the MWT cases over Alaska on 30th Dec 2015 and over Southern Greenland on 6th Jan 2016. Detailed results will be presented in the conference.