Description and evaluation of the new French operational chain of models for avalanche hazard forecasting incorporating a drifting snow scheme

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE

International audience

English. It is well known by avalanche forecasters that wind plays a determinant role in shaping the small-scale distribution of snow and strongly influences the evolution of the avalanche danger. That is why the Snow Research Center (Météo-France) has focused, over the last years, its efforts to incorporate a parameterization of the wind effects on the snowpack in its numerical modeling chain for avalanche hazard forecasting. It simulates snow redistribution between the windward and the leeward side of virtual crests and takes into account the modification of particle morphology and the sublimation of a part of the redistributed snow amount. This drifting snow scheme has been implemented in the French operational modeling chain for avalanche hazard forecasting (S2M) for the last winter season (2015-2016). New diagnosis are proposed to the avalanche forecasters including data on wind (speed and direction) and intensity of blowing snow (on a 4-level scale) for the last 24 hours and the next 48 hours. An evaluation of the interest and relevance of this application by the forecasters in the French Alps and Pyrenees is in progress. In this paper we describe the drifting snow scheme and the information provided to the avalanche forecasters. Then we evaluate the ability of this scheme to simulate the daily occurrence of drifting snow at several observation points equipped with FlowCapt sensors measuring drifting snow fluxes. We also carry out the evaluation at the experimental site of Col du Lac Blanc (2700m a.s.l) where drifting snow events are carefully monitored along the winter season.