Assessment of WAFC CB cloud top height gridded model forecasts

As part of the World Area Forecast System (WAFS) the two World Area Forecast Centres, the UK Met Office (WAFC London) and WAFC Washington, issue gridded model forecast products of aviation hazards alongside the manually-produced significant weather (SIGWX) charts. Forecasts of icing, clear-air and in-cloud turbulence, and cumulonimbus (CB) clouds are issued four times per day to the aviation community. The forecasts of deep convection cover CB horizontal extent, CB cloud base height and CB cloud top height. Recently, the forecasts from the two WAFCs were combined into a single ‘harmonised' forecast to provide greater consistency for users. In this study, the skill of the CB cloud top height forecasts has been assessed using observational data sources.

A satellite-derived cloud top height product available from the Meteosat Second Generation (MSG) satellite provides an estimate of cloud top height over the MSG footprint of Europe, Africa, the Atlantic and the Middle East. The Met Office ATDnet lightning location system fixes the position of lighting strikes based on the arrival time of unique very low frequency radio waves generated by lightning, over a domain similar to that of the MSG coverage. The satellite-derived product was used to assess the quality of the WAFC CB cloud top height forecast. Using lightning as a proxy for deep convection, the ATDnet observations were used to refine this assessment.

The results of statistical analysis of the gridded model forecasts from WAFC London and WAFC Washington, the harmonised forecast and the SIGWX charts are presented for a northern hemisphere summer period.