The Role of Latent Heat Release in Explosive Cyclogenesis: Three Examples Based on ECMWF Operational Forecasts

Abstract

Operational forecasts from the European Centre for Medium Range Weather Forecasts of three cases of explosive cyclogenesis of large magnitude that occurred in the North Atlantic during a 1-week period in January 1986 are presented, and results of numerical experiments performed on the three cases are described. Two of the cases were well predicted, and the third was not. The experiments were aimed at 1) determining the contribution of latent heat release to the explosive deepenings in the two cases that were well predicted and 2) diagnosing the cause of the poorer forecast performance in the third case. It was found that condensation heating accounted for 40%?50% of the deepening in the well-predicted cases and that most of the heating derived from stable, frontal type precipitation rather than from convective precipitation. The results of the attempt to determine the cause of the relative failure of the third forecast were inconclusive but pointed toward problems in the initial analysis. In particular, there was evidence that the initial analysis failed to capture fully the high moisture content and low static stability of the warm sector air that was ingested into the heart of the storm during the rapidly deepening stage.