Using a three-dimensional non-hydrostatic mesoscale numerical model, called Meso-NH, and starting from a large scale operational analysis, we simulate a right-moving storm produced through storm splitting. Such storms, particularly common in the Great Plains and Midwestern regions of the United States, have been less studied under other environmental context and especially over France. A better understanding of those storms is essential then, to improve their forecast. So, we study here a case that took place over northern France on 30 May 1999. That day, strong gust winds were produced over Paris and its suburbs leading to several casualties.

The simulation uses a two way interactive grid nesting with two nested models (10-km and a 2.5-km horizontal meshes). The initial state is provided by the French 3D-var ARPEGE analysis. Starting from this large scale operational analysis, the model succeeds in simulating a storm splitting that leads to a right-moving storm.

After having compared the simulation results with their observed counterparts, we made use of the simulation in order to better understand the storm dynamics. A vorticity analysis, with emphasis on stretching and tilting terms of the vertical component vorticity, has been carried out. The spatial and temporal variation of the Storm Relative Environmental Helicity has also been examined. Finally, backward and forward trajectories will help us to complete our understanding of the storm. Most of the results compare well with previous results on right-moving storms obtained from theoretical studies or numerical studies from idealized homogeneous base states. However, there exists some differences which we try to rely to the non-homogeneity of the initial state.