Seamless significant convection forecast for aviation

The Hong Kong Observatory (HKO) has been developing severe weather forecast products for the aviation community in order to provide early and reliable alerts for advance flight route, deviation and flow control planning. This study presents an 8-hour seamless significant convection forecast for the Asia-Pacific region, created by blending the extrapolation-based satellite nowcast with precipitation forecast from either the in-house regional HKO-WRF model or the European Centre for Medium-Range Weather Forecasts (ECMWF) high-resolution model, smoothly transitioning to just the NWP models thereafter.

Our 1-year verification suggested that the blended forecast benefited from heavy reliance on satellite extrapolation at early forecast hours, progressively shifting towards the NWP models as forecast lead time increased, particularly after the fourth hour when the intensity-corrected NWP model forecast outperformed the extrapolation. This study also demonstrated the advantage of the salient cross dissolve (SalCD) technique, which minimised the misses raised from linear blending. In view of the capability of the NWP models, latitude-dependent weights were developed to capture the more rapidly evolving convection at lower latitudes. A specific profile for tropical cyclones was introduced, considering that NWP models performed better with the spiral bands. The blended forecast exhibited improved accuracy compared to using only satellite extrapolation or the NWP output within the forecast period. The findings revealed the potential benefit of blending to enhance accuracy while allowing a seamless transition to the NWP models for longer lead times. In addition to the deterministic blended forecast, probability prediction was explored by perturbing the weights and combining satellite extrapolation with individual ECMWF ensemble members for supporting the decision-making of aviation users.