Numerical simulation of the 1999 Christmas day storms in Europe

The 1999 Christmas storms in Midwest Europe are analyzed in this paper. The second of the 4 low pressure systems brought strong wind and heavy rain in northern France, with a mean wind speed of 47 m/s in Paris's Orly airport. The fourth low pressure system produced similar severe storms along the western French coast and in several other countries in central and southern Europe, with wind speeds of 41 m/s in France and 55 m/s between France and Germany. Christmas days storms resulted, in the European countries, in about 140 casualties and other losses, including streets, trees, houses, and interruptions of the electrical power and telephone systems for several days. About 10,000 persons were affected by this storm, and the property damages probably reached 8,000,000,000 US dollars. As these storm had extremely violent intensity and developed fastly, the majority of the European countries' numerical forecasting centers had not provided enough early warning about the associated severe weather. Therefore, Christmas day storms have been simulated using the mesoscale numerical forecast model RAMS, and the results are analyzed in comparison with the ECMWF analyses and with the observations. The results evidentiate that RAMS can accurately simulate the main characteristics of the storms, the evolution of the low pressure, the key points of the four systems transposition and development, and the average wind fields during the storm evolution period. Simulated average wind fields are consistent with that of the meteorological observational network. The simulated storm transposition times tally with the main media's report too. The time trend of the averaged wind speeds in some specific areas calculated by RAMS demonstrate that, in the alpine region, regardless of being in the upwind or downwind sides, the storm evolutions and the values of the baric minima can be accurately simulated.