Henry's Avalanche Talk

When we get fresh snowfall, accompanied by a rise in temperatures and likely rain, the extreme danger in the days during and the hours right after the snowstorm is very apparent and often over-emphasized. Despite this initial instability, the final effect, however, is snowpack stabilisation – which is often under-emphasized.

Does this mean we ignore the obvious, classic signs of danger on a slope that is subjected to a rapid rise in temperatures and incoming solar radiation especially just after a snowstorm storm? Of course not, but equally it is important to recognise the net – final outcome of warming, melting and especially rain (any situation where free water drips down through the snowpack), will be a stabilizing ‘glueing’ effect, especially when temperatures go down below freezing level after. This is often reflected by a drop in danger level in the forecast up to the altitude at which the snowpack has been fairly well saturated – at least in the top layers down to 40-50cm. This drop in danger level (stabilisation of the snowpack) happens sometimes in as little as 12 hours after the melting or rain has ceased.

As well as this ‘glueing’ effect causing stabilisation, many steeper slopes have purged themselves of snow – often virtually down to ground level taking with it most of the facets that made up the persistent weak layer on those slopes. But the persistent weak layer, that developed during the clear skies over the two weeks leading up to the storm, is still a serious factor to consider on North’ish facing slopes up above approx 2800 m on North’ish facing slopes.

The avalanche danger levels in the N French Alps by Meteo-France show the diminishing danger level after the snowstorm on Wednesday 29th Dec, with avalanche danger ratings of 4 on the 30th, down to a 3 or 2 two days later – then down to a 1 four days later.

Images thanks to Météo-France

For more info see the article that accompanies this video on: henrysavalanchetalk.com/snowpack-stabilization-due-to-wet-snow-and-high-temperatures/

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Caroline E Elliott has worked with HAT over the years and now she has launched a book on snow safety. M

Congratulations from HAT. A great cause to keep children safe.

Off-piste snow & safety, N French Alps and surrounding areas : 17th – 23rd December 2021

Sunny weather and relatively high temperatures throughout the Alps. This should continue throughout most of next week too. Fresh snowfall may hopefully arrive at the end of next week.

Conditions range from some very crusted snow which has been affected by the higher than normal temps and wind, plus some great light powder snow in shaded / sheltered areas. Touring will start to become more necessary as the resorts gets more tracked out.

The current avalanche danger level in much of the higher parts of the Alps is 3 from about 2200m and 2 below. The 2 level will become more dominant while high North facing slopes have maintained the presence of a fairly persistent weak layer close to the ground which could facilitate triggering of a slab avalanche. Exercise care around steep North’ish facing slopes as this danger will continue to be there – however unlikely the chances of triggering are – the consequences could be very serious.

In terms of applying care, the Accident Reduction Card shown in this article and video is designed to help apply the basic points that help to make off-piste and touring reasonably safe - an acceptable risk.

https://henrysavalanchetalk.com/off-piste-snow-safety-n-french-alps-17th-23rd-december-2021/

Snow storms dying out over the weekend. Sunny and warm next week with great skiing.

It’s been a week of cold temperatures and plenty of snowfall. Snow conditions are currently excellent in the N French Alps and surrounding areas (indeed throughout most of the Alps). More snowfall is due today (Friday), dying out on Saturday – all through the Alps but mainly on the Western side. We are now able to ski down to altitudes of 1000 m or lower with snow depths deeper than normal for the time of season (a dramatic change from even a week ago, when we were wrecking our skis on hidden rocks). With an avalanche danger level of 4 out of 5 most of the week, we’ve been taking it easy and staying mainly on and around slope angles below 30°. The snow falling at the time of this writing is going to maintain the 4 to 5 danger level at least through Saturday and maybe into Sunday (mainly in the N French Alps and areas most hit by the big snowfalls) due to the storm related avalanche danger – known in the profession as ‘storm (slab) avalanches’ and some times ‘direct action avalanche’ which is the avalanche activity during and just after (about 24 hours) the snow/weather event. After this last big storm, and the direct – storm avalanche activity, the avalanche danger will drop significantly on Sunday and Monday thanks to the warming temperatures. The warming temperatures will contribute to a brief, maybe intense, cycle of instability / avalanche activity, but the net effect will be a solid stabilising of the snowpack for at least the next week.

https://henrysavalanchetalk.com/off-piste-snow-report-n-french-alps-10th-16th-december-2021/