The post Off Piste Snow Report – N French Alps – week starting 28th January 2024 appeared first on Henry's Avalanche Talk.
Off-piste snow depths above 2000 m are still above average for the time of season. You can currently ski down to around 1500 m off-piste, but with wall to wall sunshine and unseasonably mild conditions predicted this coming week, snow cover at lower altitudes will be becoming much thinner. The best off-piste snow conditions are to be found above 2500 m.
There’s no powder snow left anymore, but some nice smooth, almost ‘spring-like’ skiing conditions can be found on some of the sunnier south’ish facing slopes. On the colder more north’ish facing slopes, the snow is hard-packed windblown and some loose-sugary ‘frisette’ snow increasing with the clear nights… there are some nice strips of chauky ‘soufflé dure’ if you keep your eyes open – especially on East’ish aspects.
Pay attention on the steeper pitches with hard snow, and stay under control. The snow here is often hard and wind-blown (even icy at times). There’s a serious risk of going for a long slide, or ‘taking a whipper’ as I call it, if you slide out of control on these steep slick slopes. Watching out for ‘Terrain Traps’ – as we point out in our HAT Prevention Card and Framework -seriously applies in these potential ‘slide-for-life’ situations too (see video below).
The current avalanche danger level is around level 2 out of 5 above 2200 m, and 1 out of 5 at lower altitudes. This difference is due to the warmer slopes below 2200 m becoming more stable as they melt and refreeze.
We anticipate that with the sun-drenched, unseasonably mild week ahead with clear skies by day and night, the danger level will go down to a 1 out of 5, even on higher altitude slopes.
Long periods of clear skies will be driving changes in the snowpack, causing it to become less consolidated. This is not a problem now, but will become one after the next significant snowfall – see below.
After 6 or 7 days or so of these low temperatures and clear skies, big changes become evident in the snowpack, due to some internal layers and the surface turning into a sugary, unconsolidated, friable texture technically known as ‘facets’ due to a process known as “temperature gradient metamorphism“. Generally speaking this is when the snow surface of the snowpack becomes much colder (regularly down to around -15 to -20° C at night at the moment) than the base of the snowpack at the ground level (around 0° C). The shallower the snowpack, the more pronounced the temperature gradient between the surface and the base of the snowpack becomes and the more pronounced-faster the creation of ‘facets’, unconsolidated sugary snow, becomes.
It’s the temperature of the snow at the snow surface that counts. Air temperatures don’t need to be particularly low if the skies are clear (clear skies – especially at night – are favorable for ‘radiational cooling’ which is what helps to make the snow surface much colder than the air temperature just above it).
See this graphic (left) from ISAW La Davie, Tignes at 2800m on Sat 26th Jan, showing air temperatures of -3.6° C but surface snow temperatures at -20.5° C at 7am!!! …the clear skies at night are the main driver of these particularly low snow surface temps, but at this time of year there are still lots of slopes that spend most of the day in the shade. This maintains the snow surface temps pretty low too throughout the day.
The effect of these low surface snow temperatures will cause the snowpack to become less consolidated (sugary and incohesive in texture).
For now this is not a problem, but after the next significant snowfall lands on top of this unconsolidated snow, things will become very unstable – especially on Northerly and other shaded slopes. (When the next snowfalls come, an extra level of caution is definitely advised. For example, we add extra danger points on the scale of our HAT Prevention Card for these future ‘new snow on weak layer – after clear weather – type conditions.)
Why, you may ask, particularly on Northerly and other shaded slopes? The reason is that on shaded slopes, the snow surface temperatures stay low – unlike on slopes exposed to incoming solar radiation. Hence, during periods of clear skies, north’ish facing slopes become more unstable than south’ish facing ones. This is one explanation as to why the snowpack is consistently more unstable on Northerly and other shaded slopes than on slopes exposed to incoming radiation and above freezing temperatures. Thus the the much higher level of accidents on these North’ish slopes in Dec, Jan and Feb.
For more info on this, see one of our in-depth talks, soon available as a pre-recorded talk too.
SUN 28th: Sunny with temperatures 5 or 6°C higher than normal for the time of season. 0°C at 3300 m at the warmest part of the day. Light to moderate S wind.
MON 29th: Sunny and weather conditions almost a carbon copy of Sunday.
TUES 30th: Ditto.
WED 31st: Ditto
THURS 1st & FRI 2nd FEB: Continuing spring-like conditions. Sunny, calm and very mild for the time of season.
FOLLOWING FEW DAYS: No change.
There’s a real risk of sustaining sliding injuries on steep slick slopes this week.
Watch your speed and stay in control, otherwise you could end up going a very long way! See ‘Whipper video above’!
To keep things as safe as possible when you’re heading off-piste or ski touring, you need to apply the key safety points in our Accident Framework. Education and training is not enough : you need to apply what you know!
The Framework, which you can find in our HAT Prevention Pocket Guide, is designed to help you apply what you know. It’s a great complement to all training (and aimed at all off-piste and ski touring levels). Now available as a ‘HAT Safety Pack’, which also includes our Companion Rescue Card. The Safety Pack can be bought on our website.
The post Off Piste Snow Report – N French Alps – week starting 28th January 2024 appeared first on Henry's Avalanche Talk.
