ICAM/MAP Brig May Ten years of operational numerical simulations of snow and mountain weather conditions and recent developments at Météo-France. Y. Durand, G. Guyomarc'h, L. Mérindol, G. Giraud, E. Brun, E. Martin. Météo-France, Centre d'Études de la Neige (CNRM), 1441 rue de la Piscine, F Saint Martin d'Hères. 1)Introduction 2)The Safran/Crocus/Mepra (SCM) suite 3)Operational use of SCM (analysis and forecast modes) 4)Research use of SCM 5)Current developments 6)Conclusion 1

Main Characteristics/Limitations of the Operational SCM massif- scale avalanche hazard modeling. - homogeneous massifs (~400 km2) with different elevations (~10), aspects (7) and slopes(3) -hourly simulation of a lot of complete snow profiles (T,  Z, , LWC, stratigraphy, stability) under the assumption that, at that scale, the snowpack evolution is completely controlled by the atmospheric forcing -no realistic orography but « idealized » slopes -use only of « atmospheric » observations (no use of data concerning the snow cover) -use of NWP models: ARPEGE / ALADIN -no local small scale features forcing -crude simulation of snowdrift effects (in fresh snow crystal modification only) 2

ICAM/MAP Brig May Regional avalanche forecasting tool Analyse and forecast of the snow pack evolution by massif, elevation, aspect and slope Meteorological Data : Observations,meteo model… SAFRAN Meteorological analysis CROCUS Snow model MEPRA Expert system model 2

ICAM/MAP Brig May SAFRAN Meteorological analysis for mountain regions notions of massif, altitude, aspect 2 days forecast version by adaptation of NWP models OI and variationnal methods used Meteorological NWP model Snow and weather observations Classical meteo Observations and atmospheric sounding Analysis /6H 24H Analysis for précipitation Hourly Interpolation for all the parameters Hourly meteorological parameters affecting snowpack evolution Radar (in dev.) Satellite temperature and humidity wind velocity/ direction radiative fluxes snow and rain precipitation cloudiness 2

ICAM/MAP Brig May SAFRAN « PRACTICAL » VERSION O/I scheme and Intermittent Analysis (6h) with ARPEGE or ALADIN as guess-field for : 1. Wind (Div. + Rot.) (verticale profile + surface) 2. Humidity (verticale profile + surface) 3. Cloudiness (3 layers) 4. Temperature (verticale profile + surface) 24h Rainfall Analysis based on climatology and typical synoptic patterns. Variational Analysis at 1 hour step on 6h windows. Several algorisms and modelling for : 1. Radiations 2. Diurnal Variations 3. Vertical Snow-Rain Limits 2

ICAM/MAP Brig May CROCUS 2 1D numerical snow model

ICAM/MAP Brig May MEPRA 1D mechanical analysis –Additional mechanical characteristics, –Ram resistance profile –Shear strength profile ( C ) –Estimation of the applied shear stress (  n for snow,  s  for skier) –Wet snow instability –Slab occurrence in superficial layers, presence of buried weak layer Natural stability index Accidental stability index Natural avalanche risk on a 6 level scale (very low, low, moderate increasing, moderate decreasing, high, very high) Accidental avalanche risk on a 4 level scale (very low, low, moderate,high) Avalanche types (fresh dry, fresh wet, fresh mixed, surface slab, surface wet, bottom wet) 2

ICAM/MAP Brig May

ICAM/MAP Brig May SAFRAN Results (2) 24h analyzed rainfalls (15/11/02) 3

ICAM/MAP Brig May h forecated rainfall (11/01/99) SAFRAN Results (3) 3

ICAM/MAP Brig May /5

ICAM/MAP Brig May Tests on annual rainfall climatology (SIM Projet). Year Symposium Zoning Safran with full observation network. Safran with real-time observation network. 3/5

ICAM/MAP Brig May CROCUS results (1) 3

ICAM/MAP Brig May CROCUS results (2) 3

ICAM/MAP Brig May Scatter diagrams of measured and simulated means snow depth on 37 test sites during 4 different months over 10 winter seasons 10 years of measured (dotted) and simulated (solid) snow depths at the Tignes ski resort, Vanoise massif, 2080m. Safran-Crocus Validation (1) 3

ICAM/MAP Brig May Safran-Crocus Validation (2) Comparisons between observed and numerically simulated snowpack structures during the winter at the ski resort of "La Plagne" (Vanoise massif) on the snow pit location of "Montchavin" (2100m, NE). The different panels illustrate the weekly observed snow pits and the corresponding computed profile. The vertical axis (in cm) represents the snow depth and the blue and green curves respectively temperature and density profiles (with two different scales on the horizontal axis in °C and %V). On the right side of each profile, the stratigraphic profile is illustrated by color code while vertical hachures show crusts.

ICAM/MAP Brig May MEPRA operational results (1) MEPRA : detection of an unstable layer In this case (1st January 1996), the model has detected a snow structure favourable to an avalanche triggering by overloading (e.g. skiers). A weak layer is buried under 40 cm of new snow constituting a slab after some cohesion processes. 3

ICAM/MAP Brig May MEPRA operational results (2) MEPRA : risk of spontaneous (natural) avalanches due to an unstable fresh snow amount 3

ICAM/MAP Brig May Mepra results (3) Symbolic representation (elevation/aspects) of MEPRA natural avalanche risks in a typical spring situation (9 March 94, 12 UTC) 3

ICAM/MAP Brig May Snow and Climate Change Snow duration (1500 m ) 4

ICAM/MAP Brig May Avalanches and climate change Rainfall +10% Température +1.8°C All avalanches Melting Avalanches 4

ICAM/MAP Brig May Local avalanche forecasting tools CrocusMepra PC -Local simulation of the internal state and the mechanical stability of the snow pack - Analyse and forecast mode 4

ICAM/MAP Brig May SCALE DEFINITIONS Downscaling Massif scale : ~ 500 km 2 Time step : 1 hour Symbolic topography Local scale : ~ 1 km 2 Time step : 30 min Fine scale orography Avalanche path scale : ~ 100 m 2 Time step : ~ 5 min 5

ICAM/MAP Brig May Snow Drift Slab formation, effects of snow accumulation and erosion… Objectives : –Better estimation of accidental avalanche risks –Better localisation of avalanche risks Experimentation in a specialized field laboratory Modelling: - SAMVER : surface wind field estimation - SYTRON1 : wind transport at the massif scale (nearly operationnal) - SYTRON2 : wind transport at local scale 5

ICAM/MAP Brig May Snow Drift 5 Snow depth differences due to snow drift effects

ICAM/MAP Brig May Safran/Crocus/ Mepra chain Valuable avalanche forecasting tool for regional forecasters : meteo, snow, stability and risks « analyse » mode with all the snow/meteorological data 24 and 48 H forecast with the runs of the ALADIN and ARPEGE meteorological models and analyses by a nearest neighbour method Validations : –Meteorological (Col de Porte, Lac Blanc) –Snow depths –Snow profiles –By the avalanche forecasters 6 Conclusion (1)

The SCM chain is presently running over: 24 alpine massifs 23 Pyrenean massifs 12 islandic areas It is operationally used by numerous forecasters. It is still under development (snow drift, …) It is also a research tool (climate ….) It is used in related applications (hydrology, …) Good skiing and thank you for your attention 6 Conclusion (2)