Henry's Avalanche Talk

And a bunch of new things to come over the next few months aimed at having fun and staying safe off-piste and ski touring from all of us! Have a great spring and summer… for all of you in this N hemisphere and here’s to a great new season to those of you in the Southern!

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/