Anyone who follows the French Avalanche Bulletin will see the risk level for the Chartreuse and Grands Rousses (l’alpe d’Huez) has been revised upwards this evening to 3 (considerable) from 2. To be honest I think Meteo France has been underestimating the risk in the Chartreuse at times over the last few weeks. Today there was a serious avalanche incident on the west side of the Grand Som. A lone skier was completely buried by an avalanche. A couple of ski tourers spotted blood in the snow and were able to locate and dig out the victim who had spent a considerable amount of time under the slide. The CRS des Alpes and Security Civil attended the scene and the victim was heliported to the University Hospital in Grenoble where he is in a serious condition. Another skier triggered a slab in an exposed south facing section of the Dent de Crolles. He was unharmed by the slide.

In the Grandes Rousses the CRS/Security Civil also came to an aid of a Parisian who was buried by an avalanche under 150cm of snow close to the summit of the Rissiou above the ski resort of Vaujany. His friends were able to locate and rescue the man thanks to his avalanche beacon. The man suffered from a fractured leg and hypothermia.  A slide also crossed a ski run at Corrençon-en-Vercors at the end of the day, out of precaution the piste services checked the slide with probes and an avalanche dog.

Well you’re on the scene in the Chartreuse, and I’m not (yet). But let me offer an alternative perspective on the avalanche forecasts:

* my opinion is that there’s an over-reliance by ski tourers on a single summary number for an entire mountain group—instead of applying careful judgment to the detailed comments in the report about different layers and snowpack characteristics.

* I don’t know the details or exact location of the slide, but I would not have thought the S face of the Dent de Crolles was a place one would casually ski on a hazard level 2 day.

* I don’t know the details or exact location of the slide, but my recollection is that the W side of the Grand Som does contain a section with a slope angle (around 35-38 degrees) which many avalanche textbooks say (out of the possible range of slope angles) is most likely to release a slab avalanche.

Now most likely the ski tourers in those situations above did apply careful judgment about the details—and then just got very unlucky.
But that’s not in itself evidence that the previous avalanche report gave a wrong choice of the hazard level number . . .
Level 2 is not supposed to be roughly the same as Hazard level 1.

Glad to hear more perspectives and ideas about this.

Ken

Here is how Meteo France calculates the overall avalanche risk for natural and skier triggered slides, one thing to note: risk 5 only applies to natural avalanche risk, at this level skiing outside of open ski runs should be considered too dangerous (except maybe in nordic terrain).

I would say we were in the many specific / possible with weak load territory but it is debatable. We’ve just come out of a period of very stable conditions and now have a lot of not particularly thick slabs largely formed by the strong winds. I wonder whether the move to more detail bulletins by mountain range has changed the way the risk is estimated. The French bulletin relies on 140 observers but these are largely in ski resorts. A range like the Chartreuse perhaps lacks sufficient data for a detailed, accurate bulletin (MF has a snow study site at the col de Porte and an automatic monitoring station at St Hilaire du Touvet). Under the old bulletin risk 2 used to be pretty stable in the pre-alpes although maybe it is just the snow-pack this year. In any case skiers need to pay much more attention to the detail of the bulletin at this risk level at the moment.

Here is a comparison of risk levels and overall avalanche fatalities between France and Switzerland

Over the period 1996-2006
FR CH
1: 0%, 3%
2: 8%, 29%
3: 49%, 54%
4: 38%, 12%
5:  5%, 1%

If we are now moving towards a more Swiss style evaluation of the avalanche risk (only time will tell) then again, skiers in French ranges need to start paying serious attention to risk 2 days. Also of note, the French bulletin is issued at around 5pm the day before, the Swiss issue their bulletin on the morning of the day concerned. As Munter says, local observations on the terrain (more or less wind/snow fall) should complement the bulletin and here the new bulletin gives the estimates that they have based their assessments so it is easy to say if the risk is higher or lower and over what aspects.

I also note that there have been 3 times this season when the risk has been revised up without always a big change in the initial conditions.

To answer you question about the Dent de Crolles, no I wouldn’t ski it at risk 1… 2 or whatever when there has been a strong wind blowing from the NE for the last week. So your point about skiers seemingly not reading, or not acting on, the information in the bulletin is well made.

Here is a photo of the Grand Som avalanche taken by the CRS des Alpes

there is another slab that has broken above the cliffs that we can’t see but that possibly triggered this slide. It is a classic configuration of snow accumulation below cliffs and no doubt a weak layer formed due to the temperature gradient at this spot. Note what looks like a track on the right at mid slope, is this a ski or animal track? Anyway there are two main sets of tracks in the valley, obviously that in the center of the valley is safer but requires a bit more effort, up and down. Who hasn’t take a slightly more risky shortcut on a tour? Of course being alone was a major factor. The victim is still in intensive care and very seriously ill.

davidof - 19 February 2012 01:10 PM

The French bulletin relies on 140 observers but these are largely in ski resorts. A range like the Chartreuse perhaps lacks sufficient data for a detailed, accurate bulletin (MF has a snow study site at the col de Porte and an automatic monitoring station at St Hilaire du Touvet).

I was guessing something like that state of affairs for the Chartreuse mountain group. (And seems to me that the snowpack at St Hilaire has not much in common with the main touring areas up higher.)

One thing that backcountry skiers could do in the Chartreuse is volunteer as observers, and dig a snow pit or two each time they go out on a tour, report their snow observations in a standard format to some public site such as skitour.fr or camptocamp.org - or to Meteo France.
(The exemplary Utah Avalanche Center in USA is always asking for reports from ski tourers, despite already having like twenty times the density of automated sensors and ski resort observations as the Chartreuse. A few years ago there visiting I made a report to them).

davidof - 19 February 2012 01:10 PM

comparison of risk levels and overall avalanche fatalities between France and Switzerland over the period 1996-2006
FR CH
1: 0%, 3%
2: 8%, 29%
3: 49%, 54%
4: 38%, 12%
5:  5%, 1%
If we are now moving towards a more Swiss style evaluation of the avalanche risk ...

Or here’s two completely different interpretations of those numbers:
(B) the French + Swiss forecasters have the same philosophy of assigning hazard level numbers, but French _skiers_ are starting to act more like Swiss skiers on level 2 days. (while Swiss _skiers_ perhaps have tended to be more conservative than French skiers on level 4 days).
(C) the French + Swiss forecasters have the same philosophy of assigning hazard level numbers, but the Swiss forecasters have much better _data_ available to them.

My bottom line ... We will never know all the reasons behind the historical statistics or behind yesterday afternoon’s forecast. But it is definitely possible to get buried in an avalanche on a day that got “hazard level 2” assigned to it—so try to gather more data than the official forecast, and try to form more careful judgments about where to ski.

Also France (esp Savoie) has some great groomed cross-country ski trail networks, and it’s possible to get out for some fun + good exercise on those even when not sure how to handle the avy risk on a certain day.

Ken

davidof - 19 February 2012 01:10 PM

Under the old bulletin risk 2 used to be pretty stable in the pre-alpes although maybe it is just the snow-pack this year. In any case skiers need to pay much more attention to the detail of the bulletin at this risk level at the moment.

There’s been days this year where the text of the report and what I see on the ground give me more concern than the overall risk level might normally. But, I’ve spent more days this year under 2000m than normal although I’ve skied and climbed in this area for 20 years I’m obviously here more than usual. A lot of the big slides have been glide avalanches though and in general although they’re class 3 slides people tend not to get hurt. A lot of trees have checked out though And safety work for highways and transport etc has contributed to that increased use of explosives I mentioned the report on.

davidof - 19 February 2012 01:10 PM

Here is a comparison of risk levels and overall avalanche fatalities between France and Switzerland

Over the period 1996-2006
FR CH
1: 0%, 3%
2: 8%, 29%
3: 49%, 54%
4: 38%, 12%
5:  5%, 1%

That displacement wouldn’t like right for forecasting differences would it? You’d expect to see a one level shift wouldn’t you? ie some days might be 2 or 3, some days might be 3 or 4 but no days are likely to be 2 or 4. At the least you’d want to normalise for terrain and participants.

Interesting though, I know around 50% at CONSIDERABLE is a fairly hard figure across countries but I’d not given huge thought to other levels other than to assume (wrongly) it was also the same at around a third on MODERATE days.

davidof - 19 February 2012 01:10 PM

If we are now moving towards a more Swiss style evaluation of the avalanche risk (only time will tell) then again, skiers in French ranges need to start paying serious attention to risk 2 days. Also of note, the French bulletin is issued at around 5pm the day before, the Swiss issue their bulletin on the morning of the day concerned. As Munter says, local observations on the terrain (more or less wind/snow fall) should complement the bulletin and here the new bulletin gives the estimates that they have based their assessments so it is easy to say if the risk is higher or lower and over what aspects.

True, but the Swiss national bulletin is issued at 1700 the night before and re-issued if the conditions have altered on the day at 1000. It’s exceptionally rare (ie I can’t recall the last time) that happens and equally rare that the daily regional bulletin differs much from the earlier national one.

re interpretations of the figures as quoted above - my memory is very hazy (and my 4 month old son won’t give me time to do the research) but I remember reading/hearing something along the lines of CH communes having more ‘responsibilities’ (protecting roads etc) at L4 than FR, and hence more cost involved to each commune concerned by a L4 day - the outcome of this was that compared to FR the CH L3 encompassed more conditions at its top end (ie crept into FR L4 conditions) - or to put it another way CH L2 & L3 encompass slightly higher risk levels than FR L2 & L3.

* This is a hazy memory - facts may well be slightly off & I stand ready to be corrected/informed… *

Back to the top couple of posts the important point which is raised by KenR is that the number is almost meaningless without the detail behind it (as a guide mate of mine who teaches avvy courses is fond of drumming into his clients - “what does L3 Mean?” - “Considerable” - “Yes but what does considerable mean? - Which slopes, which aspects, what time of day? etc etc”.  The text of the BRA is all important, as is the knowledge of the prior weather conditions…

offpisteskiing - 20 February 2012 10:18 AM

re interpretations of the figures as quoted above - my memory is very hazy (and my 4 month old son won’t give me time to do the research) but I remember reading/hearing something along the lines of CH communes having more ‘responsibilities’ (protecting roads etc) at L4 than FR, and hence more cost involved to each commune concerned by a L4 day - the outcome of this was that compared to FR the CH L3 encompassed more conditions at its top end (ie crept into FR L4 conditions) - or to put it another way CH L2 & L3 encompass slightly higher risk levels than FR L2 & L3.

You are right, in the top matrix the (Large / Some) box has a 3 in it in the Swiss matrix for exactly this reason. There is also the fact that the bulletin, both French, Swiss and US/Canada has to respond to both mayors/civil security and recreationalists. I see on the forums this has caused some confusion with a number of level 5 days in the winter which quickly dropped to level 2. Level 5 due to natural purges down avalanche couloirs, level 2 because the underlying snowpack was relatively stable.

KenR -

(B) the French + Swiss forecasters have the same philosophy of assigning hazard level numbers, but French _skiers_ are starting to act more like Swiss skiers on level 2 days. (while Swiss _skiers_ perhaps have tended to be more conservative than French skiers on level 4 days).

Some experts say this is down to a more rigorous use of methods such as Munther (3x3, reduction) by Guides and the Swiss Alpine Club. In the French FFME clubs there is now an increasing emphasis on the 3x3 method (regional, zonal, local risks) with a lot of training happening over the last couple of years.

All I can say is Praise the Lord and Pass the me my ABS . Erm not that I have an ABS but you can see in incidents like the Grand Som above it would have saved a lot of pain.

re ABS if you apply an industrial risk assessment to off piste skiing then an ABS (or similar) airbag would be prioritised over a transceiver… (Don’t have time to explain the full works right now but am preparing something on this for my website/blog...).

To maybe respond to what Simon said a bit more for the same period as above here is the frequency that each level was used between France and Switzerland. Of course snow pack and weather differences may explain all these differences but we certainly see a reluctance to use level 4 and above as Simon suggests. This also seems to confirm what KenR says, 38% of French fatalities at level 4 which concerns only 8% of days. Too many people getting out right after fresh snow or high winds on inappropriate routes.

FR, CH
1: 13%, 17%
2: 42%, 50%
3: 37%, 31%
4: 8%, 2%
5: <1%, <1%

offpisteskiing - 20 February 2012 10:47 AM

re ABS if you apply an industrial risk assessment to off piste skiing then an ABS (or similar) airbag would be prioritised over a transceiver… (Don’t have time to explain the full works right now but am preparing something on this for my website/blog...).

yeah, I agree, we discussed this a while ago

http://pistehors.com/news/forums/viewthread/767/#2591