Avalanche Awareness and off piste skiing tips from Henry's Avalanche Talk

Complicated situation evolving

Since we last wrote there has been at least another 30cm of new snow.  When the recent snow fell it was wet and heavy (see Roddy's reports)

 

Also we just heard on radio that English snowboarder got killed in avalanche in Tignes in the Tufs couloir. When we get some more info, we will post it on the blog.

 

It is now a complicated week for conditions and stability.  The risk level is 3 above 2000m.  This means that natural avalanches are unlikley but a single skier could trigger an avalanche when on any 30 degree or steeper slope oir when crossing at the base of a steeper slope.

 

There have been relatively few slides given how much snow fell, but be careful, as well as the Tufs incident today we know of another incident on the orientation table route on Bellevarde where a seasonnaire got taken over a small cliff and survived but was very shaken.

 

On the brighter side, the wet and heavy snow has all dried out above 2000m due to a dry clear night and there is plenty of nice snow to be had if you know where to stay safe.  If you are not sure play on lower angle slopes and keep an eye out for steeper slopes above you or convexities below you.

 

The Guides may be seen on the steeper slopes, since some of them are OK, but if you do not know how to tell which is OK and whihc is not then play safer when the bulletin shows a risk level fo 3.

 

The situatrion is likely to change rapidly but it is hard to predict.

 

If it stays warmish as forecast for the next 2 days, then the current snow will settle well and form a good layer for the next snowfall to bond with.  But this may not happen and our big advice is to track the conditions each day to see how the base layer evolves.  If you do that, then you will be in a stronger position to judge how unstable the situation will be when the next snow arrives on Friday night Saturday morning.

 

We are expecting some good colder snow on Saturday early morning provided the cold front from the west makes it through to displace the southerly weather system we have predicted for Thursday and Friday.

 

The longer term outlook shows more snow later next week on Monday and Wednesday.  There will be plenty of great skiing to be had.  Spotting where it is safe is a bigger challenge.

 

2 top tips

Track what happens to the current snow as the weather changes over the next 2 days

Stay on lower angle slopes if you are not sure about the risks until it is clearer that the risk levels have subsided.

 

Finding the best snow

Finding the best snow off piste when it has not snowed for 10 days and the snow has suffered wind damage can be quite a challenge and the best tip may well be just to get a professional guide.  Last week we discussed how you can look out for patches of good snow and by working out the slope aspect angle and altitude, you will be able to translate this into insights about where to find good snow.

 

The sunshine will affect slopes with different slope angle in different ways.  North facing steeper slopes will have very little sun in December January and will hold the powder for longest.  At present these slopes have powdery snow that is turning very grainy day by day or has been compacted by the wind.  This could create a weak layer underneath the next snow fall, we are watching to see what happens here.  Low angle North facing slopes tend to be wind affected and have a wind crust that is fine to ski on if you do not break through, but if you break through it can be challenging

On the south side it is different.  South facing steep slopes face the sun directly and deteriorate fast.  The sun's intensity is magnified per square centimetre due to the angle of the slope and facing the sun.   Lower angle south facing slopes have an angle to the sun and the sun works more slowly. (this is especially true in the morning before the sun has done its full damage.).  The bulletin highlights some risks on this slopes at the moment.  Interestingly some of the best powder and our video of people making powder turns was done on South east facing slopes

West facing slopes catch the warmer afternoon rays and can deteriorate badly.  See photo of recent slide in the Pays Dessert in Val d'Isere.

East facing slopes get the morning rays which will tend to be weaker and exist in lower temperatures.  So east facing slopes will hold soft powdery snow for longer.

If you not have a good grasp of which is North South East and East (or even if you do) a compass can be a great help to spot which slopes face where.  Given that nuances of slope aspect (10 degrees) can make a big difference, then the compass help even the most aware and experience people.

But within a single slope, there will be lots of different aspects which will produce different snow conditions across the breadth of the slope.  Here the nuances of slope angle become apparent.  So when you have decided to go down a slope, there can be big differences between one side and another or even in different parts of the track as you go down.  Have you ever followed a good guide and then deviated from his path and as a result found yourself in much poorer snow than the others experienced.  This can be true even if you are only 10m to the left or right of his track.  This is due to the nuances of slope aspect.

What you can do here is to practice looking at the slope and studying how the snow conditions change as you ski through it.  These observations will form the basis of your next judgement about where it is best to go.

Sunshine - slopes that face the sun may suffer snow melting even if they are above the freezing level. The sun can warm the surface of the snow.  So you need to take account of this when estimating where you might find good snow.  There is no magic formula for this.  You may often notice your guide banging the snow on the edge of the pistes with his sticks.  This will be to test the snow condition at any given altitude or aspect.  By reading the conditions you find as you ski, this will help you predict where the best snow will be.

Over the past 3 weeks we have covered a lot of ground about how to find the best snow.  The headline points have been.

• Get some good information - recent weather patterns, advice from experts, this is essential for you to know which of the factors have been at play over the past week
• Know how to understand the impact of the different factors

1. Wind
2. Temperature
3. Slope Angle
4. Slope aspect
5. Altitude

Look at what you find as you ski and update your understanding with real evidence gathered as you ski not just using predictions based on your analysis.

It may all sound very complicated, and clearly the experts have built up considerable experience that enables them to work out where the best snow is.  But in the meantime, you too can apply some of this thinking to improve your skiing experiences.  Even if you begin to think through some of these points you will get yourself into better snow conditions than if you do not

Read the actual conditions

Read the actual snow conditions and you can predict where the snow will be best

 

We have seen quite a few changes to the snowpack over the past week,  It has been one of those weeks where you cannot rely on the advice of your mates who tell you they found great snow yesterday in place xxx.  The wind and sun can change it all very rapidly and what was good yesterday may not be good tomorrow.  You have to read the conditions both before you go and when you get out there.

 

Any good off piste guide will know about the recent weather and recent snow reports and may well have advice from his team colleagues.  But you will always see them go and look at the actual conditions when they get out there.  When you see good snow (or bad snow) make a note of the altitude and aspect and shelter.  It is likely that in the same circumstances elsewhere, you will find similar quality of snow.  Today I found perfect powder in sheltered bowls facing south east at around 2500m in Tignes.  This was replicated later on Bellevarde.

 

The other evidence to look for is obvious signs of danger.  There are a number of small cornices with wind loaded slopes underneath.  This could be deduced by looking at the wind direction and the shape of the snow on the slope.  On 2 occasions we avoided crossing some 35 degree slopes with great powder just because we were not sure about the effect of wind loading.  A more experienced guide may have deemed it OK, but we were not sure so we played safe

Staying safe in avalanche risk level 4

In these conditions one of the best ways to stay safe and have more fun is to think not just about where to go but about "how you go".  Don't get smitten by "powder frenzy".  there are a number of points around this and the exact decision must be based on a judgement about where you are, the size of the group, the skill of the group, the fitness of the group and the general mood and attitude.  But these three points always matter and remain important.

• Ski one at the time, - this reduces the pressure on the slab and dramatically decreases the chances you will trigger the slab to slide 
• Cluster together and wait for your friends only in islands of safety
  
• Don't ski above other skiers,.  To trigger an avalanche on to someone else is a few steps worse than bad manners, you might end up in court for manslaughter.

Often this is the difference between an avalanche and an accident.  These factors are even more important in risk level 4 - which is where we are right now

What does the Hazard rating scale mean?

You will know that we expect all off piste skiers to read the avalanche bulletin and understand the risk level that is present on each day.  This is about understanding the avalanche bulletin and interpreting the risk level. 

   

Today, you will see the risk is described as Marque, or Considerable which is level 3 on a scale of 1-5.

To help understand this, we have published in this ezine two versions of the scale for your study.  There is one published by Sport Scotland Avalanche information service which is written in English in its original form.  There is also a translation of the French scale published by the ValdIsere authorities.

   

At our session with our technical director this week.   Alain Duclos  explained one of the risks you can manage if you know the hazard rating.    Avalanches usually only happen on slopes above 30 degree slope angle.  But there is a quite significant risk that you can trigger an avalanche on a steeper slope above you, even if you are on a slope that has a gentle slope angle that is lower than 30 degrees.  This risk is magnified when the rating is higher.  So

• Risk level 1 - you cannot trigger a slope that is above you. you can only trigger a slide on slopes that are greater than 30 degrees and then only in a few places.
• Risk level 2 - it is highly unlikely you could trigger a slide, if you remain on slopes with a lower angle than 30 degrees.
• Risk level 3 - it is quite likely you can trigger a slide on a slope above you even if you are on a slope angle that is less than 30 degrees.  So make sure you go one at a time.
• Risk level 4 - You should keep well away from slopes above 30 degrees.  If the slope has a weakness and you ski underneath it, you could set it off.  If you have to risk it, then ski one at a time and make sure the group clusters around islands of safety.

This is another way you can use the hazard rating scale.

   

Hazard Rating from Sport Scotland Avalanche Information Service

   

At HAT we like these Avalanche risk descriptions, we are less sure of their prognosis for whether you should go off piste or not.  For us the scale is about helping you make decisions and should be read in conjunction with the local bulletin.  It cannot be translated into a simple conclusion as they do here.

   

Degree of hazard	Snowpack stability	Avalanche probability	For off-piste & back-country activities
1 (low)	The snow pack is generally well bonded and stable.	Triggering is possible only with high additional loads2 on a few very steep extreme slopes4. Only a few small natural6 avalanches (sluffs) possible.	Virtually no restrictions on off-piste & back-country skiing & travel.
2 (moderate)	The snow pack is moderately well bonded on some1 steep3 slopes, otherwise generally well bonded.	Triggering is possible with high additional loads2, particularly on the steep3 slopes indicated in the bulletin. Large natural6 avalanches not likely.	Generally favourable conditions. Routes should still be selected with care, especially on steep3 slopes of the aspect5 and altitude indicated.
3 (considerable)	The snow pack is moderately to weakly bonded on many1 steep3 slopes.	Triggering is possible, sometimes even with low additional loads2. The bulletin may indicate many slopes which are particularly affected. In certain conditions, medium and occasionally large sized natural6 avalanches may occur.	Off-piste and back-country skiing and travel should only be carried out by experienced persons able to evaluate avalanche hazard. Steep3 slopes of the aspect5 and altitude indicated should be avoided.
4 (high)	The snow pack is weakly bonded in most1 places.	Triggering is probable even with low additional loads2 on many steep3 slopes. In some conditions, frequent medium or large sized natural6 avalanches are likely.	Off-piste and back-country skiing and travel should be restricted to low-angled slopes; areas at the bottom of slopes may also be hazardous.
5 (very high)	The snow pack is generally weakly bonded and largely unstable.	Numerous large natural6 avalanches are likely, even on moderately steep terrain.	No off-piste or back country skiing or travel should be undertaken.

Notes

1 Generally described in more detail in the avalanche bulletin (e.g.altitude, slope aspect, type of terrain, etc.).

2 Additional load: high - e.g. group of skiers, piste machine, avalanche blasting.low - e.g. skier, walker.

3 Steep slopes: slopes with an incline of more than30 degrees.

4 Steep extreme slopes: those which are particularly unfavourable in terms of the incline, terrain profile, proximity to ridge,smoothness of underlying ground surface.

5 Aspect: compass bearing directly down the slope.

6 Natural: Without human assistance.

Why you should track the evolution of the snowpack

Tip of the week

In order to be able to judge where it is safe to go and where there is a risk of triggering an avalanche, it is necessary to track the evolution of the snow pack in the few weeks prior to your ski trip.

At the start of the season, we are watching to see if the snow falls steadily and creates a secure and stable base.  This season, the snow fell in cold conditions in November but since then it has become humid with mild weather.  This will cause the snow to compact and bind itself to the slope.

Whereas last year, the weather remained cold after the snowfall.  This led to the development of depth hoar on the surface of the snow.  When the next fall of snow arrived it fell on top of the depth hoar.  This created a weak layer in the snow and this was responsible for a number of avalanche accidents in January.

We will watch to see if the depth hoar develops and keep you up to date.