Objective verification of manual and automated forecasts of clear air turbulence from World Area Forecast Centres

The two World Area Forecast Centres (WAFCs) are responsible for providing meteorological hazard forecasts to aviation customers around the world. The forecasts are presented in graphical format as Significant Weather (SIGWX) charts.

The desire from the international aviation community for a gridded product, more suitable for ingestion into flight planning systems, led to the development of automated gridded forecasts produced in gridded binary (GRIB) format. These have been distributed on a trial basis by the two WAFCs for several years.

Until now little objective verification has been available for the forecaster produced WAFC SIGWX or automated GRIB WAFC products. The increasing availability of high resolution aircraft observations now makes routine objective verification of clear air turbulence (CAT) forecasts a possibility. In particular 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 (ROC) analysis to investigate the skill in both the operational SIGWX and new GRIB CAT forecasts from both WAFC London and WAFC Washington. Global verification results using GADS data are presented from a three-month winter period from November 2008 to January 2009.