Ensemble forecasting of snowpack conditions and avalanche hazard

Abstract The prediction of avalanche hazard involves an analysis of current snow conditions, the upcoming meteorological conditions and their combined impact on the future state of the snowpack. The SAFRAN–SURFEX/ISBA-Crocus–MEPRA (S2M) chain of numerical models is used by avalanche forecasters in France to estimate present and future avalanche hazard over areas assumed to be meteorologically homogeneous (massifs), primarily as a function of altitude. Until now, the meteorological forecast data provided to S2M comes from the deterministic numerical weather prediction model ARPEGE with a lead-time of 2 days. In this study, we introduce the application of ensemble meteorological forecasting to avalanche hazard forecasting by using the output of an ensemble of 35 ARPEGE predictions to feed S2M and thus provide an ensemble of 35 different predicted snowpack conditions. A posteriori ensemble forecasts were generated and evaluated in the French Alps for the winter 2013–2014 with 4 days lead time, initialized each day at 6 UTC. Forecasts over the Pyrenees during the exceptional winter and spring 2012–2013 were also carried out. Results indicate that accounting for the uncertainty in meteorological forecast significantly improves the skill and the usefulness of the model chain, regardless of the prediction lead time. The predictability of snowpack conditions using the ensemble forecast technique remains good at a 4 day lead time. These results provide the foundation for the development of probabilistic estimates of simulated avalanche hazard levels for operational avalanche hazard forecasting.

[1]  P. M. Fôhn.  The stability index and various triggering mechanisms , 1987 .

[2]  O. Talagrand,et al.  Evaluation of probabilistic prediction systems for a scalar variable , 2005 .

[3]  Anton H. Westveld,et al.  Calibrated Probabilistic Forecasting Using Ensemble Model Output Statistics and Minimum CRPS Estimation , 2005 .

[4]  Neill E. Bowler,et al.  The MOGREPS short‐range ensemble prediction system , 2008 .

[5]  E. Martin,et al.  A meteorological estimation of relevant parameters for snow models , 1993 .

[6]  Yves Durand,et al.  Towards a new chain of models for avalanche hazard forecasting in French mountain ranges, including low altitude mountains , 2013 .

[7]  Charles R. Sampson,et al.  A New Method for Estimating Tropical Cyclone Wind Speed Probabilities , 2009 .

[8]  G. Thirel,et al.  On the Impact of Short-Range Meteorological Forecasts for Ensemble Streamflow Predictions , 2008 .

[9]  F. Molteni,et al.  The ECMWF Ensemble Prediction System: Methodology and validation , 1996 .

[10]  Ice.  The international classification for seasonal snow on the ground , 1990 .

[11]  G. Brier.  VERIFICATION OF FORECASTS EXPRESSED IN TERMS OF PROBABILITY , 1950 .

[12]  P. L. Houtekamer,et al.  Increasing the horizontal resolution of ensemble forecasts at CMC , 2003 .

[13]  E. Martin,et al.  The detailed snowpack scheme Crocus and its implementation in SURFEX v7.2 , 2012 .

[14]  Nicolai Meinshausen,et al.  Quantile Regression Forests , 2006, J. Mach. Learn. Res..

[15]  H. Scheffé.  The Analysis of Variance , 1960 .

[16]  Yves Lejeune,et al.  Impact of a climate change on avalanche hazard , 2001, Annals of Glaciology.

[17]  A. Montani,et al.  A spatial verification method applied to the evaluation of high‐resolution ensemble forecasts , 2008 .

[18]  A. H. Murphy.  A New Vector Partition of the Probability Score , 1973 .

[19]  Christopher A. T. Ferro,et al.  Comparing Probabilistic Forecasting Systems with the Brier Score , 2007 .

[20]  B. Efron.  Bootstrap Methods: Another Look at the Jackknife , 1979 .

[21]  Craig H. Bishop,et al.  The THORPEX Interactive Grand Global Ensemble , 2010 .

[22]  Alain Joly,et al.  PEARP, the Météo‐France short‐range ensemble prediction system , 2015 .

[23]  G. Thirel,et al.  Short‐ and medium‐range hydrological ensemble forecasts over France , 2010 .

[24]  E. Martin,et al.  A computer-based system simulating snowpack structures as a tool for regional avalanche forecasting , 1999, Journal of Glaciology.

[25]  A. Raftery,et al.  Using Bayesian Model Averaging to Calibrate Forecast Ensembles , 2005 .

[26]  Roberto Buizza,et al.  The Singular-Vector Structure of the Atmospheric Global Circulation , 1995 .

[27]  G. Giraud.  MEPRA - An Expert System for Avalanche Risk Forecasting , 1992 .

[28]  Inger-Lise Frogner,et al.  Limited‐area ensemble predictions at the Norwegian Meteorological Institute , 2006 .

[29]  E. Kalnay,et al.  Ensemble Forecasting at NCEP and the Breeding Method , 1997 .

[30]  Florian Pappenberger,et al.  Application of a medium-range global hydrologic probabilistic forecast scheme to the Ohio River Basin , 2011 .