If you want to go into the mountains but don't think you've mastered all the things we've just discussed, we advise you to get training and contact mountain professionals to learn the different techniques and gain experience in the mountains with them, little by little, so that you can become autonomous.
Where does the Avalanche Risk Scale come from?
The Avalanche Risk Scale was created in 1993 to harmonise avalanche risk forecasting in the countries of the Alpine Arc.
The EAWS Avalanche Risk Matrix:
This is a table that forecasters use according to the snowpack and climatic hazards. They imagine whether there will be more or fewer avalanches, whether they will be larger or smaller, and whether they will be easy or difficult to trigger.
This table has been adopted by all the major meteorological organisations in order to standardise avalanche risk forecasting!
If you look at this table, you'll realise that the avalanche scale is exponential depending on the slopes involved, and that forecasting is more complex than you might think at first!
Depending on the topography of certain slopes, the avalanches that start in these areas are always much bigger than on other slopes. If you're in an area where when an avalanche starts, the whole side of the mountain can go, you have a much greater risk than on a small slope, so take this into account, along with the topography of the slopes, when the snow accumulates in a hole it's also a more exciting situation than if the snow spreads out at the end of the slope...
The figure only gives an idea of the stability of the snowpack!
Then, depending on the topography of the slopes and their gradient, the risk or potential danger varies greatly!
Local Avalanche Risk (RLA):
Where does the RLA come from?
For a long time, forecasters, guides, ski patrollers and other mountain professionals have been discussing the risk of avalanches.
The scale is exponential, one risk 3 can be very different from another, and many mountain professionals talk about potential danger.
The risk of avalanche changes with altitude, as do temperatures, winds and precipitation.
In a ski area, it always takes longer to open the higher altitude zones because the risk is greater at higher altitudes because the winds and precipitation are higher and the temperatures colder, and you gradually climb higher...
Each altitude sector has its own snowpack characteristics and this is a factor that is also easy to respect: if you decide not to exceed 2600 metres in altitude, you won't go above it. An itinerary often varies in terms of exposure when the itinerary is a little complex.
In local forecasting, the winds, temperatures and precipitation are estimated for different altitudes, and the snowpack is also very different depending on its altitude. Based on these parameters, I develop a local risk by altitude on a time scale, this is the Local Avalanche Risk (LAR).
Avalanche risk management is complex, just as weather models are becoming increasingly refined with the advent of fine models (Arôme, etc.). I think that avalanche risk will evolve by refining the risk scale and taking better account of different altitudes.
The Local Avalanche Risk Matrix by altitude (RLA):
I've used the EAWS matrix, which is recognised worldwide by snow experts and the meteorological services of the main countries, and I've added a + to the high end of each risk level to indicate that the risk is at its highest.
Given that we are on a spatial scale reduced to the Les Arcs - La Plagne area, we can refine the forecast, but be aware that the Avalanche risk is calculated for mountain areas (the most dangerous and least frequented zones).
The + indicates that the avalanches are more numerous or of a size that is significant for the risk.
This system takes time to stabilise, making it easier for users to understand that the scale is exponential and making it easier to translate avalanche risk forecasts.
In snow, certainty must be replaced by risk management where questioning is essential with an idea of the probability of an avalanche starting. Just because a slope hasn't started doesn't mean you haven't taken risks.
The different sizes of Avalanches :
Where do avalanches trigger?
Avalanches need slope to be triggered; the areas where avalanches are triggered where the slope is the smallest are around 25 degrees of slope.
All professionals start to be wary of avalanches with a slope of 30° or more at any risk, but depending on the level of risk, the zone where avalanches are triggered will be mainly on slopes of varying steepness:
Risk 1: Avalanches are triggered mainly on steep slopes of 40° or more, but as a general rule the risk of the slope becoming unstuck is greater than the risk of an avalanche in risk 1.
Risk 2: Avalanches are triggered mainly on steep slopes of 40° or more.
Risk 3: Avalanches are triggered mainly on moderately steep slopes of 35° or more, distance avalanches are possible.
Risk 4: Avalanches are triggered mainly on slopes of 30° or more, there are lots of remote avalanches.
Risk 5: Avalanches are triggered mainly on slopes of 25° and more. A simple slope can present a real risk and sometimes a simple fall through the thick snow cover can present a risk of drowning at the foot of trees or other terrain accidents without outside help.
The special case of creeping and seracs :
Creeps:
These are areas where the snowpack is cracked and the area slides more or less slowly.
The risk of avalanche is high in these areas, so we advise you to avoid them at all times.
As a general rule, creep is found in pastures or areas of smooth rock, mainly to the south, but also to the east and west.
Areas of scree and north-facing slopes are rarely subject to creep and from 2800 metres they become very rare and are absent on glaciers.
Seracs:
For mountaineers, seracs are part of the objective risks, like rockfalls. A serac fall causes a very high overload which can trigger a large avalanche if the snow conditions are not very stable (Risk 1) and it is therefore better to avoid these areas.
The available RLA avalanche risk does not rate these two types of avalanche, so in risk 1 and 2 with creep or serac falls you can observe avalanches of much greater size than the EAWS or RLA avalanche matrix.
Creeps and seracs are zones with an objective danger to be avoided or else it is very important to limit the time spent under these zones.
Who produces this weather report?
It's produced by Jean Luc Quey, who is a Pisteur Secouriste 2 ème degré Artificier and Nivo Météo at Les Arcs ski resort!
He's also a mountain leader, paraglider, climber and mountain enthusiast.
He's been lucky enough to go to Nepal many times to lead and supervise high-altitude treks. Thierry Arnou's weather routing enabled us to be in the valley when Cyclone Hudhud hit on 17 October 2014 (140 deaths on the Annapurna, Manaslu and Naar Phu trekking routes).
This experience, in which 250 mm of rain fell on us in 36 hours, bringing 2 to 3 metres of snow to the high altitude passes, made me think a lot about risk management in the mountains and forecasting extreme phenomena. We often talk about averages, but weather forecasting is above all a science that can alert people when an annual, decennial, centennial or millennial phenomenon is coming, and depending on the activities you do, a much more detailed forecast is needed to carry out your activities with a margin of safety.
This bulletin is only an aid to decision making, in the mountains you will be solely responsible for your actions at your own risk, if the situation does not seem to conform to the forecast, adapt and take the necessary decisions, the bulletin gives a lot of information on the amount of snow expected depending on the altitude and winds if the values are higher then the dangers will be greater.
I was lucky enough to work with the forecasters from Météo France to produce the BERA for ten years in Les Arcs, taking soundings and readings at the station and with my other colleagues in the meteorological forecasting field. I gained a lot of experience from these numerous exchanges and I would particularly like to thank Thierry Arnou, Michel Malgrand and all the ski patrollers in Les Arcs for these exchanges.
I'm continuing to take readings and analyse the snowpack at Les Arcs, and for a long time now I've been producing a local forecast for the resort, which is now available on the Esprit Montagne website to give Paradiski skiers a local analysis to complement the BERA from Météo France.
