Coiffier, Jean (Service Central d'Exploitation de la Meteorologie, Meteo-France)
Since about six years Meteo-France's Forecasts Offices have been issuing warning messages toward Civil Security Services in case of severe weather events. Strong winds and storms, heavy precipitations, thunderstorms, snowfalls, freezing rains, cold outbreaks and avalanches are the meteorological phenomena, which can become dangerous when their intensity overstep several thresholds. In these case the Regional Forecast Offices issue special warning messages specifying the chronology of the phenomena, the expectd maximum value of the corresponding meteorological parameters and the geographical area (list of French Departments) which can be affected by these severe events.
Since two years both Meteo-France and the French Civil Security Services have been undertaking a systematic evaluation of the efficiency of these warning messages. On one hand the observed characteristics of the meteorological event (begining of the significative event, duration, recorded peak values, affected areas) are compared with the observed consequences of the event (number of interventions, importance of the emergency actions, damages to the buildings, rescue operations, injured or died people) are collected by the Civil Security Services. The treatment and the comparision of all these informations allows to assess the pertinency of the warning procedures according to each geographical area. The examination of the results shows that the southern part of France is often affected by severe meteorological phenomena originating from the Mediterranean area:
strong winds, heavy precipitations and thunderstorms. It also appears that the Forecast Offices have difficulties to properly handle convective events: If they generally succeed in defining the area which is likely to be concerned by the convective phenomena, they are not able to define the exact location of its maximum strenght.
These problems lead either to issue the warning too late, or to extend the warning area with the risk of increasing the number of false alarms. Severe events originating from the Mediterranean area illustrate the dilema, the Forecast Offices are facing on. The study also gives some insight into the difficulties in establish a link between a forecast meteorological phenomenon and its consequences.