Scottish Avalanche information Service


The General Snowpack Situation - Winter 2011/12

The SAIS winter season started early in December 2011 with a weekend report service being provided in the Northern Cairngorms and Lochaber areas. The first winter storms arrived late October at summit levels, with natural avalanche activity reported on Ben Wyvis, then more significant snowfall later in November. In early December a weak but limited snowpack caught out the unwary with a number of avalanches being triggered by parties in Creag Meagaidh and Corrie na Lochain in the Northern Cairngorms, fortunately without consequence. High winds and snowfall presented areas of windslab and considerable to high avalanche hazard reports being issued.

This was a reminder that one should be mindful of avalanche hazard from the first day of a winter. Many avalanche services worldwide recognise that the early part of the winter presents a challenge for forecasting. Keen winter enthusiasts often forget to consider avalanches in their first days of activity, sometimes with fatal consequences. In the latter part of December the snowcover, which promised a good winter to come, was ravaged by mild conditions, very strong winds and a deep thaw. Throughout January, cycles of snowfall with cold conditions was followed by warm temperatures and thaws. This became the general pattern with short term, natural avalanche activity, occurring in all areas.

Colder conditions, very strong winds and drifting snow arrived for a period in the latter part of January. This presented a snowpack that increasingly developed weaknesses at depth. To the observer, the snow cover seemed limited in area and of little consequence. Furthermore, the surface conditions were becoming more firm, which gave an impression of stability when walked or skied on. At depth though, the shallow snowpack and prolonged cold air temperatures, promoted the growth of square shaped grains, that produced a slowly thickening weak layer of facets ( a sugar like grain) and worsening snowpack instability. Clear calm conditions enticed many enthusiastic climbers and skiers into the hills, 24 avalanches where triggered by people over a 20 day period between 19 January and 9 February (with 14 triggered in 4 days from 4-7 Feb). The avalanches occurred predominantly in the eastern regions of the Highlands, fortunately without serious consequence. (Go here for more info on the snowpack conditions: here)

From mid February to the end of March the snowpack thawed and a period of sunny, spring like conditions prevailed. The snowpack diminished in extent, with remnants lingering only in the highest corries and shaded gullies. March end, through April and into May, saw the return of winter conditions which, unusually for spring, presented a cold snowpack and short term instabilities during storm cycles. The SAIS forecast season was extended well into May with weekend forecasts being provided in Lochaber and Northern Cairngorms until the 19th May. During this period, snow cover provided late winter opportunities for skiers, climbers and walkers, with a skier triggered avalanche occurring in the Northern Cairngorms during a period of short term instability immediately after a storm, early morning on the 13th May. Warmer conditions arrived in late May and this signaled the end of winter.

SAIS Operation

Avalanche Hazard information is provided on a daily basis in the 5 main mountain areas of Scotland. Avalanche hazard assessment is achieved by traveling in the mountains on foot or by ski and carrying out snow profiles and field tests, noting many factors which, when combined, present an indication of the current avalanche hazard. On return to base, weather forecasts, provided to us by the Met office forecaster team in Aberdeen, are used for further information. An avalanche hazard forecast is determined, and after discussion between the SAIS forecasters and the Co-ordinator, an avalanche hazard report is published.

The avalanche reports are provided by SAIS Avalanche Forecasters who have many years experience of avalanche hazard assessment, in most cases over 15 years. They have undergone an SAIS verification process, meet the relevant SAIS observer and forecaster standards and undergo continual professional development. Additionally, forecasters are very experienced and committed climbers, skiers and outdoor enthusiasts competent in all the skills necessary for safe travel in the most challenging of winter conditions. The team comprise Mountain Guides, Instructors and Avalanche Experts from many countries. Their experience and professionalism is integral to providing the best avalanche forecasting service possible to all persons that engage with the winter mountain environment of Scotland.

Avalanche Hazard Information Reports

The most significant factor regarding the number of observed hazard days for the winter of 2011/12 was the period, mid March onwards, when the snowpack diminished in most areas to insignificant amounts. This resulted in no hazard forecasts being issued in all areas for periods between 6 - 12 days.

For the charts above, the number of hazard days shows a reasonable consistency between all five areas. For approximately 40-50% of the days in Lochaber (48 days) and the Northern Cairngorms (55), the hazard level was at Considerable or above and, in other areas 24% - 30% of the days.

The moderate level of hazard occurred for approximately 26-34% of the winter days. Human triggered avalanches are still a possibility at this level of hazard, something that may not normally be considered. Many national avalanche warning agencies worldwide recognise, that the Moderate level of hazard presents strong potential for catching people out. The mountain traveller may be off guard, the areas of instability are often more limited in area and may only be present in isolated, steep places, usually high up in corries. Additionally, although the snowpack may be moderately stable and or limited in area, the size of a group and its spacing becomes critical. People can load a snowpack with their combined weight and the triggering of an avalanche becomes greater . Moderate levels of hazard therefore still require vigilance, and a good spacing out of group members to minimise the loading on a slope.

Avalanche Occurrences

Recorded avalanches are generally a compilation of observed avalanche occurrences from SAIS observers in the 5 areas of operation and submitted reports from winter mountain activists and non mountain users.

The SAIS avalanche reporting facility on the website helps greatly with the collation of occurrences, the public are able to send details of avalanche observations which, once verified, provides additional information. Reliable avalanche observations require good visibility and clear identification, in this respect avalanche occurrences can only be recorded where people have access or can clearly see avalanche evidence from roads and paths.

There are many places in mountain terrain where people do not travel, and during bad weather when visibility is poor. Therefore it can be assumed that a greater number of avalanche occurrences have taken place than have been recorded.

The recording of avalanche occurrences is the best indicator of the immediate short term snow stability situation. Avalanche occurrence location and the reporting of avalanche incidents is therefore very valuable in enabling the SAIS to pass on good information to the public, provide snowpack stability verification, and to illustrate the extent of avalanche occurrences.

The Total number of avalanche occurrences recorded by the SAIS for the winter of 2011/12 was 154. Of this number, 127 were natural and 33 were triggered by persons. Of the 33 triggered by persons: 4 avalanche occurrences were purposefully triggered by ski patrol or SAIS observers during the avalanche hazard assessment process, 6 were triggered by skiers and boarders and 23 were triggered by climbers/walkers.

Reaching the Public

In the early part of the winter a new mobile phone application was launched, which enables the SAIS reports to be viewed on the move. The facility can be accessed by pointing a phones web browser to

Additionally, information such as: weather forecasts, webcams, definition of avalanche hazard and its implication for mountain travelers, as well as travel advice in avalanche terrain, can also be found on the new mobile site.

During the period from launch in late January 2012 to season end, the mobile phone daily avalanche reports were viewed 25836 times.

Research and Development

Snow and Ice Mechanics

Dr Jane Blackford runs a snow and ice mechanics research group in the School of Engineering at The University of Edinburgh. A central theme in their research is understanding how the fine-scale structure (microstructure) of snow and ice influences large-scale behaviour.

Understanding the properties of snow not only helps us in understanding how avalanches release but can also be applied to the many ways in which we interact with snow in our every day world, from rubber tyre contact on snow covered roads to surfaces and materials in buildings and clothing that are contacted by snow.

Dr Jane Blackford outlines their recent work:

“We have projects on fundamentals of snow deformation, winter sports, and rubber friction on snow and ice. For the work on snow deformation, Tom Barraclough (a PhD student in the group), has designed and built novel instrumentation and measurement techniques for laboratory snow experiments under controlled conditions. The output of the experiments provides insights into the inhomogeneous deformation of snow. Snow deforms differently in different locations – you can notice this inhomogeneous deformation when you stand on snow and it squeaks. The majority of our work is laboratory based – in purpose built cold rooms – and uses artificial snow as a consistent reproducible starting material; we also make studies and comparisons with natural snow. We use techniques to examine the microstructure of snow and ice including optical microscopes, and a low temperature scanning electron microscope that enables us to image the structure at very fine length scales (see images of natural and artificial snow). These techniques allow us to examine how the microstructure of snow changes with time and temperature. We relate this to processes that occur in real environments and to the properties of the particular microstructures. The behaviour of snow in avalanches or of vehicles on snow-covered roads is complex; a challenge in our work is to extract the essential features of the real systems and design controlled scientific experiments to investigate the fundamentals and to make predictions of behaviour.”

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