A common misconception about avalanche accidents is that they’re mainly related to rising temperatures. When I ask people about when and where they think most avalanche accidents occur, they nearly always reply ‘In Spring, on South facing slopes’. It’s an understandable theory because these wet snow avalanches can be frequent, spectacular and destructive. However, as far as most avalanche accidents go, the vast majority involve cold, dry slab avalanches triggered by the victim(s) in December, January and February on North’ish facing slopes (in the N. Hemisphere).
We emphasise this fact to counter the widespread misunderstanding that avalanche danger is mainly related to rising temperatures.
Having said that, it is still important to take note of a rise in temperature, rain, etc., because it often creates serious instability, especially when it’s the first big temperature rise above freezing and/or rain of the season on a previously cold, dry snowpack. The resulting avalanche cycles can be very dangerous, and yes, there are accidents that contribute to a significant minority of the total avalanche accidents each year.
The net 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 rating up to the altitude at which the snowpack has been fairly well saturated. This drop in danger rating (stabilization of the snowpack) happens sometimes in as little as 12 hours after the melting or rain has ceased.
Why does this ‘wet/humid avalanche scenario’ not contribute to most avalanche accidents where people are involved? I believe this is because common sense works well in wet snow, melt-freeze, scenarios – if one can be bothered to use it, e.g. not going onto closed runs, roads and paths when ‘nothing happens most of the time‘. Although these types of avalanches don’t claim as many lives as cold, dry slab avalanches do, they still need to be treated with serious respect as the video below demonstrates.
In sum, the danger from rapid warming, rain, etc. is the obvious, conspicuous ‘known’ enemy. The more deadly enemy is the covert, quiet trap of the cold, dry slab avalanche, that you may unsuspectingly walk (ski or snowboard) into despite subtle but clear and ‘obvious’ clues indicating danger.
This video by Aaron Cassells shows a near miss when a wet snow avalanche came down across a CLOSED walking track, narrowly missing a person below. We’ve noticed that many accidents involving wet snow avalanches involve people in closed areas – closed due to avalanche danger.
Here in the N French Alps, it’s been another week of heavy snowfall. We already have substantial snow depths, recent snowfalls and more snowfall forecast (snow/rain limit of 1400-2800m in the N French Alps and surrounding areas over the next days). For the next few days, temperatures will be climbing considerably, with snow/rain continuing on and off. By the end of 3 Feb / Wednesday night, it is predicted that freezing level will have risen to 2800 m and crazy mild temperatures are expected for Thursday too (0° C at around 2900 m in the day, and barely falling at night!), even milder on Friday and Saturday before it starts cooling down again.
When we see a rapid rise in temperature, such as this, along with rain, snow, sun etc., this will create a risk of spontaneous, natural avalanches – especially just after a rain or snowstorm. Some of these could be very large and spectacular. They will not be triggered by skiers but will happen naturally, especially below 2300m. With ski lifts currently closed, and the snow becoming very humidified, heavy and difficult to ski, there will probably very few off-piste skiers around the next few days, but there will be a real threat to roads, walking paths and buildings. Anyone at the bottom of a steep slope will be at risk until temps drop again.
Natural wet snow avalanches that release on steep slopes due to rain and a big increase in temperatures, during and just after snowstorms, can and do cause tragic accidents. We’ll need to keep an eye on this over the next few days – as well as the other issues of long term instability caused by cold temperatures, the persistent weak layers(s), that we’ve been harping on about all season long.
As mentioned above, the net outcome of this warming and especially rain, wherever free water has dripped down through the snowpack, will be a stabilising ‘glueing’ effect, especially when temperatures go down below freezing level again. You may notice that even within 12-24 to 48 hours of this warming episode/rain, the avalanche danger rating will drop by at least one level on the scale.
Starting early next week, it’s going to get colder again. So this will help the stability of the snowpack a lot, especially up to altitudes where the warming and rain has saturated the snowpack a good amount (we estimate up to 2400 m in the N.French Alps and surrounding areas). However, whenever there’s a persistent weak layer(s), like now, there’s still a serious potential for unexpected releases, so stay vigilant!
Safety is Freedom!
There’s a long list of evidence that shows how applying simple frameworks, checklists and memory aids reduce risk in ‘high consequence, low feedback’ risk contexts prevalent in: aviation, military, finance, health care, avalanche terrain etc.
See our HAT quick reference ‘Safety is Freedom Framework’ for accident reduction in avalanche terrain. The Framework is aimed at all levels of off-piste and touring: for beginners: a point of departure; for experts: a guide for further learning; for pros: it’s a great framework for client training and quick memory aid.
The Framework is best if accompanied by training such as HAT events and on-snow courses, but it’s also a useful companion for all training as it focuses on the basic key points that all avalanche training courses address – it helps you to keep focused on the essential accident reduction points.