Objective verification of World Area Forecast Centre clear air turbulence forecasts

The two World Area Forecast Centres (WAFC) are responsible for providing aviation hazard forecasts above 800 hPa (6000 ft) including clear air turbulence (CAT) to aviation customers around the world. A new automated gridded forecast for CAT is now being produced by the two WAFCs along with the traditional forecaster-produced Significant Weather (SIGWX) charts. Until now little objective verification has been available for the WAFC products. However, the increasing availability of high-resolution in situ aircraft observations now makes routine objective verification a possibility. The Global Aircraft Data Set (GADS) formed from the fleet of British Airways Boeing 747-400 aircraft is a particularly useful resource. This paper proposes an objective verification scheme using Relative Operating Characteristic analysis to investigate the skill in both the operational SIGWX and new gridded CAT forecasts from both WAFC London and WAFC Washington. Global verification results using GADS data are presented for 4 months during winter November 2008 to February 2009.