Numerical simulation of the northern Germany storm of 27-28 August 1989

On 27 August 1989, an unusual mesoscale storm struck the area between Hamburg and Kiel in Germany. Locally, more than 100 mm of precipitation fell in 24 h, and mean winds exceeding 25 m/s^-1 were recorded. The operational models failed to predict both the development of the originally innocent-looking low, and its track. Successful simulations have been performed for this situation by introducing the Sundqvist scheme for parameterization of the hydrological cycle into the Norwegian operational limited area model. The simulations show that latent heat release is the main driving mechanism in the intensification of the low. Comparison between simulations with and without released latent heat taken into account shows significant differences in the development and also in track, and clearly demonstrates the role of released latent heat in generation and clustering of the PV, and its subsequent importance for spinning up the mesoscale vortex.