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Avalanche bulletin through Friday, 15 November 2019
In the south a lot of fresh snow. Outside marked and open pistes a high avalanche danger will be encountered in some regions
Edition: Th. 14.11., 17:00 Next update: Fr. 15.11., 17:00 Validity
Avalanche bulletin through Friday, 15 November 2019
In the south a lot of fresh snow. Outside marked and open pistes a high avalanche danger will be encountered in some regions
Edition Th. 14.11., 17:00 Next update Fr. 15.11., 18:00 Validity
Avalanche bulletin through Friday, 15 November 2019
In the south a lot of fresh snow. Outside marked and open pistes a high avalanche danger will be encountered in some regions
Edition Th. 14.11., 17:00 Next update Fr. 15.11., 17:00 Validity
Avalanche bulletin through Friday, 15 November 2019
In the south a lot of fresh snow. Outside marked and open pistes a high avalanche danger will be encountered in some regions
Edition Th. 14.11., 17:00 Next update Fr. 15.11., 17:00 Validity
Level 4, high
Fresh snow
Avalanche prone locations
In all aspects above approximately 2400m.
Danger description
Much of the fresh and wind-drifted snow represent the main danger. As a consequence of the heavy snowfall more frequent natural avalanches are to be expected during the course of the night, even very large ones in isolated cases. In the typical avalanche paths they can reach intermediate altitudes. Transportation routes situated at higher altitudes in particular can be endangered occasionally. The conditions are very critical for backcountry touring and snowshoe hiking outside marked and open pistes.
Gliding avalanches
An increasing number of gliding avalanches are possible on very steep grassy slopes.
Level 3, considerable
Fresh snow
Avalanche prone locations
In all aspects above approximately 2400m.
Danger description
The fresh snow represents the main danger. As a consequence of a strong southerly wind, avalanche prone wind slabs will form during the night as well. Avalanches can be released easily and reach large size in isolated cases. In addition individual natural avalanches are possible, this applies in particular during the night. Backcountry touring calls for experience in the assessment of avalanche danger and caution.
Gliding avalanches
Gliding avalanches are possible on very steep grassy slopes.
Level 2, moderate
Wind slabs
Avalanche prone locations
In particular in west to north to east facing aspects above approximately 2400m.
Danger description
The wind slabs represent the main danger. They are to be found in particular in gullies and bowls, and behind abrupt changes in the terrain. Avalanches can in some places be released by people and reach medium size. The wind slabs are to be evaluated with care and prudence.
Level 3, considerable
Wind slabs
Avalanche prone locations
In particular in west to north to east facing aspects above approximately 2400m.
Danger description
The fresh and older wind slabs represent the main danger. As a consequence of the sometimes storm force wind they will increase in size additionally during the night. Avalanches can be released easily and reach medium size. The wind slabs are to be avoided as far as possible. Backcountry touring calls for experience in the assessment of avalanche danger.
In the south a lot of fresh snow. Outside marked and open pistes a high avalanche danger will be encountered in some regions
Edition: 14.11.2019, 17:00 / Next update: 15.11.2019, 18:00
Snowpack
Above 1000 to 1500 m there is snow covering the ground over widespread areas. With snow depths of 50 to 80 cm at 2500 m, most
of the snow is found on the Main Alpine Ridge from the Monte Rosa region as far as Ofen Pass. In the remaining regions of
Switzerland, with the exception of glaciated high alpine zones, the snow cover is for the most part still thin and irregular.
Over the last few days, loosely-packed fresh snow and old snow was initially transported by northerly winds, subsequently
on Thursday by southerly winds. This snow was deposited in gullies and bowls and behind terrain rolls. On Thursday night as
a result of very intensive snowfall on the Main Alpine Ridge and southwards therefrom, together with strong to storm-strength
southerly winds, large-sized and area-wide snowdrift accumulations are expected to form.
Observed weather on Thursday, 14.11.2019
In the eastern regions it was quite sunny, in the other regions of Switzerland skies were heavily overcast for the most part.
In the morning hours in the Jura, the Valais sector of the Main Alpine Ridge and in the western part of Ticino, light precipitation
set in, which intensified as evening approached. The snowfall level in the northern regions lay at 800 to 1000 m, in the southern
reigons at 600 to 800 m.
Fresh snow
By Thursday evening in the western part of the Jura, in the western sector of the Main Alpine Ridge, in the Gotthard region
and in the western part of Ticino: 5 to 10 cm from place to place;
Temperature
At midday at 2000 m, between -1 °C in the foehn-influenced regions of the north; and -5 °C in the southern regions.
Wind
Winds were blowing from southerly directions,
-
at moderate to strong velocity, at strong to storm-strength in the northern sector of the Alpine Ridge,
- in the northern Prealps and in the furthermost southern regions, at light to moderate strength.
Weather forecast through Friday, 15.11.2019
On Thursday night on the Main Alpine Ridge and southwards therefrom, persistent and heavy snowfall is anticipated. The snowfall
will spread also to the regions immediately north of the Main Alpine Ridge, however the precipitation will be less intensive
there. Further to the north, snowfall will tend to decrease, in the foehn-influenced regions of the north it will presumably
remain dry and bright skies will prevail as a result of foehn influence. On Friday morning, the snowfall will move into the
Engadine and subsequently in the other regions of Switzerland slacken off during the course of the day. The winds are also
expected to slacken off somewhat. The snowfall level in the upper valleys of the Ticino will drop down to the valley floors
during Thursday night. In the other regions of Switzerland the snowfall level will lie at 800 to 1000 m.
Fresh snow
Between Thursday evening and Friday evening, in the southern regions above approximately 800 m, in the northern regions above
approximately 1200 m:
- Main Alpine Ridge from Monte Rosa over the Simplon region and southern Goms into southern Urseren, upper valleys of Maggia, Main Alpine Ridge from Val Bregaglia into the Bernina region: 60 to 80 cm;
- remaining regions of the Main Alpine Ridge from Great St. Bernard into the Upper Engadine and southwards therefrom, Riederalp region: 40 to 60 cm;
-
north of the Main Alpine Ridge and the regions bordering the Riederalp region, remaining parts of the Engadine, Val Müstair:
20 to 40 cm;
-
remaining regions of the northern flank of the Alps, of the Valais and Grisons: 10 to 20 cm, in the Prealps and in the Jura
only a few centimetres, or else it will remain dry.
Temperature
At midday at 2000 m between -3 °C in the northern regions and -5 °C in the southern regions.
Wind
- On Thursday night, strong to storm-strength winds from southerly to southeasterly directions, in the Alpine valleys of the north strong foehn wind will prevail.
- During the course of the day, winds will slacken off somewhat, be blowing at moderate to strong velocity from southerly to southwesterly directions.
Outlook through Sunday, 17.11.2019
On Saturday on the Main Alpine Ridge and southwards therefrom, skies will be predominantly overcast and above approximately
900 m a small amount of intermittent snowfall is anticipated. In the northern regions, it will be partly sunny, accompanied
by some cloudbanks. On Sunday, skies will be predominantly overcast. A small amount of intermittent snowfall is anticipated
in the eastern and southern regions more than anywhere else. The snowfall level in northern regions will be at 600 m, and
in southern regions at 1000 m.
The avalanche danger levels are expected to incrementally decrease. In the areas of major precipitation, hardly any naturally-triggered, dry-snow avalanches are to be expected. At high altitudes, winter sports participants and mountain climbers can still trigger avalanches, including large-sized ones in the major areas of precipitation.
The avalanche danger levels are expected to incrementally decrease. In the areas of major precipitation, hardly any naturally-triggered, dry-snow avalanches are to be expected. At high altitudes, winter sports participants and mountain climbers can still trigger avalanches, including large-sized ones in the major areas of precipitation.
Your observations can improve the quality of the avalanche bulletin. We are very grateful for any reports and photos received.
Please report your observations of avalanches or alarm signs, or your estimation of the avalanche danger, or simply send us a picture illustrating the current situation. Your report from the field will be considered along with all the other information when we assess the avalanche danger. It is impossible, however, to reflect the exact content of each individual report in the avalanche bulletin.
The best way to file a report is by completing the interactive form on this page. If your report is to be used in the 5 pm avalanche bulletin, it should be submitted before 2:30 pm if possible. Reports received later will normally be given consideration in the next assessment.
Other reporting options:
- White Risk App
- E-mail to lwp(at)slf.ch
- Freephone number 0800 800 187
In the south a lot of fresh snow. Outside marked and open pistes a high avalanche danger will be encountered in some regions
Edition: 14.11.2019, 17:00 / Next update: 15.11.2019, 18:00
Snowpack
Above 1000 to 1500 m there is snow covering the ground over widespread areas. With snow depths of 50 to 80 cm at 2500 m, most
of the snow is found on the Main Alpine Ridge from the Monte Rosa region as far as Ofen Pass. In the remaining regions of
Switzerland, with the exception of glaciated high alpine zones, the snow cover is for the most part still thin and irregular.
Over the last few days, loosely-packed fresh snow and old snow was initially transported by northerly winds, subsequently
on Thursday by southerly winds. This snow was deposited in gullies and bowls and behind terrain rolls. On Thursday night as
a result of very intensive snowfall on the Main Alpine Ridge and southwards therefrom, together with strong to storm-strength
southerly winds, large-sized and area-wide snowdrift accumulations are expected to form.
Observed weather on Thursday, 14.11.2019
In the eastern regions it was quite sunny, in the other regions of Switzerland skies were heavily overcast for the most part.
In the morning hours in the Jura, the Valais sector of the Main Alpine Ridge and in the western part of Ticino, light precipitation
set in, which intensified as evening approached. The snowfall level in the northern regions lay at 800 to 1000 m, in the southern
reigons at 600 to 800 m.
Fresh snow
By Thursday evening in the western part of the Jura, in the western sector of the Main Alpine Ridge, in the Gotthard region
and in the western part of Ticino: 5 to 10 cm from place to place;
Temperature
At midday at 2000 m, between -1 °C in the foehn-influenced regions of the north; and -5 °C in the southern regions.
Wind
Winds were blowing from southerly directions,
-
at moderate to strong velocity, at strong to storm-strength in the northern sector of the Alpine Ridge,
- in the northern Prealps and in the furthermost southern regions, at light to moderate strength.
Weather forecast through Friday, 15.11.2019
On Thursday night on the Main Alpine Ridge and southwards therefrom, persistent and heavy snowfall is anticipated. The snowfall
will spread also to the regions immediately north of the Main Alpine Ridge, however the precipitation will be less intensive
there. Further to the north, snowfall will tend to decrease, in the foehn-influenced regions of the north it will presumably
remain dry and bright skies will prevail as a result of foehn influence. On Friday morning, the snowfall will move into the
Engadine and subsequently in the other regions of Switzerland slacken off during the course of the day. The winds are also
expected to slacken off somewhat. The snowfall level in the upper valleys of the Ticino will drop down to the valley floors
during Thursday night. In the other regions of Switzerland the snowfall level will lie at 800 to 1000 m.
Fresh snow
Between Thursday evening and Friday evening, in the southern regions above approximately 800 m, in the northern regions above
approximately 1200 m:
- Main Alpine Ridge from Monte Rosa over the Simplon region and southern Goms into southern Urseren, upper valleys of Maggia, Main Alpine Ridge from Val Bregaglia into the Bernina region: 60 to 80 cm;
- remaining regions of the Main Alpine Ridge from Great St. Bernard into the Upper Engadine and southwards therefrom, Riederalp region: 40 to 60 cm;
-
north of the Main Alpine Ridge and the regions bordering the Riederalp region, remaining parts of the Engadine, Val Müstair:
20 to 40 cm;
-
remaining regions of the northern flank of the Alps, of the Valais and Grisons: 10 to 20 cm, in the Prealps and in the Jura
only a few centimetres, or else it will remain dry.
Temperature
At midday at 2000 m between -3 °C in the northern regions and -5 °C in the southern regions.
Wind
- On Thursday night, strong to storm-strength winds from southerly to southeasterly directions, in the Alpine valleys of the north strong foehn wind will prevail.
- During the course of the day, winds will slacken off somewhat, be blowing at moderate to strong velocity from southerly to southwesterly directions.
Outlook through Sunday, 17.11.2019
On Saturday on the Main Alpine Ridge and southwards therefrom, skies will be predominantly overcast and above approximately
900 m a small amount of intermittent snowfall is anticipated. In the northern regions, it will be partly sunny, accompanied
by some cloudbanks. On Sunday, skies will be predominantly overcast. A small amount of intermittent snowfall is anticipated
in the eastern and southern regions more than anywhere else. The snowfall level in northern regions will be at 600 m, and
in southern regions at 1000 m.
The avalanche danger levels are expected to incrementally decrease. In the areas of major precipitation, hardly any naturally-triggered, dry-snow avalanches are to be expected. At high altitudes, winter sports participants and mountain climbers can still trigger avalanches, including large-sized ones in the major areas of precipitation.
The avalanche danger levels are expected to incrementally decrease. In the areas of major precipitation, hardly any naturally-triggered, dry-snow avalanches are to be expected. At high altitudes, winter sports participants and mountain climbers can still trigger avalanches, including large-sized ones in the major areas of precipitation.
Have you observed alarm signs or an avalanche?
Your observations can improve the quality of the avalanche bulletin. We are very grateful for any reports and photos received.
More information about observations
Please report your observations of avalanches or alarm signs, or your estimation of the avalanche danger, or simply send us a picture illustrating the current situation. Your report from the field will be considered along with all the other information when we assess the avalanche danger. It is impossible, however, to reflect the exact content of each individual report in the avalanche bulletin.
The best way to file a report is by completing the interactive form on this page. If your report is to be used in the 5 pm avalanche bulletin, it should be submitted before 2:30 pm if possible. Reports received later will normally be given consideration in the next assessment.
Other reporting options:
- White Risk App
- E-mail to lwp(at)slf.ch
- Freephone number 0800 800 187
No avalanche bulletins are being published at the moment. Nevertheless, you should still stay up to date with the avalanche situation in the mountains, especially if there is fresh snow.
However, the SLF will, by way of exception, also issue avalanche bulletins in the summer in case of heavy snowfall. There are different ways you can be notified when these bulletins based on the snow situation are published:
- by push alert on SLF's free White Risk mobile app: appearing in four languages (English, German, French and Italian), this can be downloaded from iTunes App Store (for iPhones) or Google Play Store (for Android);
- by mobile text message (SMS): please send an SMS with the message START SLF SOMMER to the phone number 9234 – you can cancel this service at any time by sending an SMS with the message STOP SLF SOMMER; cost: CHF 0.20 per SMS;
- via an RSS feed which informs you whenever an avalanche bulletin is published.
Depending on the snow and avalanche situation, the regular publication of avalanche bulletin recommences in November/December.
Have you observed alarm signs or an avalanche?
Your observations can improve the quality of the avalanche bulletin. We are very grateful for any reports and photos received.
More information about observations
Please report your observations of avalanches or alarm signs, or your estimation of the avalanche danger, or simply send us a picture illustrating the current situation. Your report from the field will be considered along with all the other information when we assess the avalanche danger. It is impossible, however, to reflect the exact content of each individual report in the avalanche bulletin.
The best way to file a report is by completing the interactive form on this page. If your report is to be used in the 5 pm avalanche bulletin, it should be submitted before 2:30 pm if possible. Reports received later will normally be given consideration in the next assessment.
Other reporting options:
- White Risk App
- E-mail to lwp(at)slf.ch
- Freephone number 0800 800 187
Danger levels
The SLF uses the five-level European avalanche danger scale to indicate the avalanche danger. The danger level is worked out on the basis of a range of variables, in particular the avalanche triggering probability, the prevalence of avalanche prone locations and the avalanche size. A danger level always applies to a region and not to one particular slope. The danger level given in the avalanche bulletin is always a forecast and should be checked on- site.
Avalanche danger scale
Short version
Danger level | Characteristics | Recommendations for backcountry recreationists |
5 very high | Disaster situation Numerous very large and extremely large natural avalanches can be expected. These can reach roads and settlements in the valley. | You are advised not to engage in winter sports beyond open ski runs and trails. Very rarely forecast. Around 1 % of avalanche fatalities. |
4 high | Very critical avalanche situation Natural and often very large avalanches are likely. Avalanches can easily be triggered on many steep slopes. Remote triggering is typical. Whumpf sounds and shooting cracks occur frequently. | Stay on moderately steep terrain. Heed runout zones of large avalanches. Unexperienced persons should remain on open ski runs and trails. Forecast only on a few days throughout the winter. Around 10 % of avalanche fatalities. |
3 considerable | Critical avalanche situation Whumpf sounds and shooting cracks are typical. Avalanches can easily be triggered, particularly on steep slopes with the aspect and elevation indicated in the avalanche bulletin. Natural avalanches and remote triggering can occur. | The most critical situation for backcountry recreationists. Select best possible route and take action to reduce risks. Avoid very steep slopes with the aspect and elevation indicated in the avalanche bulletin. Unexperienced persons are advised to remain on open ski runs and trails. Forecast for around 30 % of the winter season. Around 50 % of avalanche fatalities. |
2 moderate | Mostly favourable avalanche situation Warning signs can occur in isolated cases. Avalanches can be triggered in particular on very steep slopes with the aspect and elevation indicated in the avalanche bulletin. Relatively large natural avalanches are not to be expected. | Routes should be selected carefully, especially on slopes with the aspect and elevation indicated in the avalanche bulletin. Travel very steep slopes one person at a time. Pay attention to unfavourable snowpack structure (persistent weak layers, old snow problem). Forecast for around 50 % of the winter season. Around 30 % of avalanche fatalities. |
1 low | Generally favourable avalanche situation No warning signs present. Avalanches can only be triggered in isolated cases, in particular on extremely steep slopes. | Travel extremely steep slopes one person at a time and be alert to the danger of falling. Forecast for around 20 % of the winter season. Around 5 % of avalanche fatalities. |
Full description of the European avalanche danger scale
This scale, introduced by the European Avalanche Warning Services in 1993, defines the danger level based on the snowpack stability and the avalanche triggering probability. The full description of the scale also includes other columns that have not been internationally agreed relating to typical characteristics, recommendations and consequences.
European Danger Scale with recommendations and additions (.pdf)
Danger levels – a simplified picture of reality
The avalanche danger do not increase in linear fashion from one level to another, but disproportionately. In this context
- the snowpack stability, and with it also the additional load required to trigger an avalanche, decreases, and the avalanche triggering probability increases;
- the prevalence of avalanche prone locations increases, meaning that there are more locations where avalanches are released naturally or can be triggered;
- the avalanche size increases.
If the additional load required to trigger an avalanche decreases and there are also more locations where avalanches can be triggered, the avalanche triggering probability increases. This is also shown by the stability distribution in the chart below.
In a typical case, all these influencing variables change as indicated above. This means that in the case of a 'low' avalanche danger, usually only small avalanches are triggered in just a few locations and mostly only due to a high additional load, while in the case of a 'high' avalanche danger, a lot of avalanches, some of them very large, are triggered or are released naturally (without human assistance).
However, there are also atypical situations that do not fit into this picture. These are detailed in the next section.
Various characteristics of avalanche danger
Also in the case of less typical avalanche situations the danger level is a measure of the order of magnitude of the avalanche danger. These situations are detailed below along with information about their assessment by the avalanche warning service. As these are atypical situations, no list can ever be exhaustive. In atypical situations deviations from the danger level definition are inevitable. These are set out as far as possible in the avalanche bulletin's danger description.
Faceted-crystal snowpack
In the case of low avalanche danger (level 1) the snowpack is normally well bonded and stable. However, after long periods of fine weather with shallow snow, another form of snow occurring in mid-winter which makes slab avalanches virtually impossible is the whole snowpack being loose and transformed into faceted crystal. The snowpack is then very weak and there are weak layers, but the bonded layer above (the 'slab') is missing. With no bonded layer a fracture cannot be propagated, meaning that there is no possibility of a slab avalanche forming. This means there is a low avalanche danger (level 1), despite or precisely because of the very loose snowpack. 'Stable snowpack' means 'not liable to trigger slab avalanches' and does not refer to the hardness of the layers.
This situation is not a good omen for the future, given that as soon as it is snowed on, the fresh-fallen snow and fresh snowdrift result in the creation of a 'slab' where one did not exist before. Underneath this is the loose old snowpack in the form of a substantial weak layer. The avalanche danger will increase significantly, generally resulting in a long-lasting old-snow problem.
Small, easily triggered snowdrift accumulations
Fresh snowdrift accumulations can often be triggered by individual winter sports enthusiasts. The size of the snowdrift accumulations depends not only on the wind but also on the supply of fresh and old snow which can be transported. For only little snow which can be transported, the snowdrift accumulations are usually so small that getting buried by them is unlikely. In this case, level 2 (moderate) is often used despite the high probability of triggering an avalanche. In such situations the snowdrift accumulations can usually be seen in good visibility by the trained eye. They need to be avoided especially on terrain where there is a danger of falling.
Old-snow problem with a significant weak layer deep down in the snowpack
The more thickly a weak layer is covered, the more difficult it becomes for a fracture to form there. This is most likely to occur in locations where the snow is relatively shallow or at transitions from shallow to deep snow. In the case of an old-snow problem with a significant weak layer deep down in the snowpack, avalanche prone locations are usually relatively rare. However, avalanches often reach large size, and are therefore particularly dangerous for winter sports enthusiasts. Therefore, the avalanche danger in the case of an old snow problem can sometimes be considerable (level 3) even if the avalanche prone locations are fairly rare. An aggravating factor is that the avalanche prone locations are barely recognisable in old snow situations, even to the trained eye. In the case of weak old snow, more fatalities can be expected than in the case of the other avalanche problems (at the same danger level).
'Skier high'
If numerous large and, in many cases, very large natural avalanches can be expected, the avalanche danger is classified as 'high' (level 4). Under such circumstances, exposed locations (usually sections of transport routes, and in isolated cases also buildings) can be put at risk. In addition to this classic 'road high', there is a further variant of this danger level where very large avalanches are hardly expected (e.g. because there is still too little snow at the start of the winter) but a lot of medium and large avalanches are naturally released and can be triggered very easily at multiple locations. In the case of this 'skier high', winter sports enthusiasts are in severe danger away from secured ski runs. By contrast, transport routes are unaffected or only affected in isolated cases.
Avalanche activity in case of wet and gliding snow
Wet-snow avalanches are rarely triggered by people, while in the case of gliding avalanches this is virtually impossible. Therefore, natural triggering is the main cause of such avalanche types even in the case of the lower danger levels. The maximum possible naturally triggered avalanche activity, based on the defined danger level, relates mainly to wet-snow and gliding-snow conditions and less to conditions involving dry avalanches. In this context large natural avalanches are possible when there is a moderate danger of wet-snow or gliding avalanches. In the case of a situation with dry-snow avalanches, such naturally triggered avalanche activity normally corresponds to a considerable avalanche danger, as then avalanches are also expected to be triggered by individuals.
Change in the avalanche danger as the day progresses
The avalanche danger changes over time and may not reach or overshoot the boundary between one danger level and another within the period of validity of the avalanche bulletin. Normally the danger increases, for example due to snowfall or wind, significantly quicker than it recedes again.
If the danger level is likely to change during the day, the level published in the avalanche bulletin and the danger description normally show the situation in the morning. The change (often an increase) is indicated in the danger description. Here are some examples:
- "The avalanche danger will increase and reach level 3 (considerable) in the afternoon." In this case, level 2 (moderate) is marked on the hazard map.
- "Danger level 4 (high) will be reached during the morning." In this case, level 4 (high) is marked on the hazard map.
- "As a consequence of daytime warming and solar radiation, wet-snow avalanches can be expected again from the middle of the day below approximately 2400 m." (With no danger level indicated)
If the avalanche danger is assessed to be level 4 (high) or even level 5 (very high) at night, and then one level lower during the day, the morning rule is deviated from. As when transport routes are in danger, the avalanche danger is also significant at night, the higher avalanche level that applies during the night is given in the evening edition. In the morning edition this is then reduced to the level applying in the morning.
Double map
In typical springtime conditions, the danger of wet-snow avalanches along with daytime warming and solar radiation will increase significantly as the day progresses. During the day the danger of dry-snow avalanches will usually only change slightly in these conditions. Thus, while in the morning dry-snow avalanches are the main danger, in the afternoon the main danger is posed by wet-snow avalanches. In this situation, two maps show both the more favourable morning situation (dry-snow avalanches) and the unfavourable situation in the afternoon (wet-snow avalanches as the day progresses). The transition from one map to another cannot be pinned down to a specific time. It depends on the conditions and the altitude and also in particular the aspect. While on the east-facing slopes the danger of wet-snow avalanches will already increase during the morning, this will usually only occur later on the west-facing slopes.
In special cases a double map is also used if there is a significant danger of gliding avalanches, and this danger is greater, over a wide area, than the danger of dry slab avalanches. It is worth noting in this case that these two dangers do not vary significantly during the day. Therefore, the two avalanche types are possible throughout the day.
Additional information
Avalanche danger and risk
The avalanche bulletin describes the avalanche danger, i.e. the triggering probability and the possible size of avalanches in a specific region, but the exact timing of an avalanche being triggered and the actual length of its starting zone and fracture depth cannot be determined.
An avalanche danger only becomes a risk (i.e. a probability that damage will occur) if endangered individuals, animals, forest, infrastructure etc. are in the area of the potential avalanche. In the avalanche bulletin, the avalanche danger is assessed regardless of the presence of endangered individuals or objects, i.e. on weekends with fine weather and weekdays with poor weather alike, and for populated areas and open terrain alike.
If an avalanche is released somewhere on a glacier during a snowstorm, there would obviously be an avalanche danger, but there would be no risk if there were no people in the surrounding area. If the same avalanche is released on a popular touring route on a sunny weekend, the risk will be much greater. The danger given in the avalanche bulletin may be the same in both cases, but the risk will be different.
Avalanches are a very special natural hazard, given that unlike flash floods or earthquakes the 'perilous process' of an avalanche can be initiated by human activity. If anyone comes onto a dangerous slope, the artificial additional load can trigger an avalanche. In the case of more than 90% of the snow sports enthusiasts buried by a slab avalanche, they triggered the avalanche themselves or it was triggered by another member of their group.
Frequency of danger levels
The most frequently forecasted danger level in the Alps is level 2 (moderate), accounting for almost half of days (per warning region). It thus captures a day with 'average' avalanche danger. Level 3 (considerable) is forecasted on about one third of days. Danger level 4 (high) is only forecasted on 1% of winter days on average, while level 5 (very high) is forecasted even more rarely. In the Jura, the lower danger levels are more frequent.
The avalanche danger will change gradually whereas the scale has levels.
The danger scale has five levels. However, in reality the avalanche danger changes gradually. This means there is a range within each level.
Further Information
Division into regions
The warning regions used by MeteoSwiss and all the Swiss federal government's other official natural hazard warning authorities form the basis for the division into regions. Groups consisting of several warning regions are formed, generally by applying climatological or political criteria, yielding overarching region names (see the maps below).
Great care is required when interpreting references in the context of backcountry tours in regional border areas. For example, the Jungfrau region is usually accessed from the north (northern flank of the Alps or Eastern Bernese Oberland), but the backcountry touring area mostly lies in Northern Upper Valais.
Marginal areas
There are no clearly defined boundaries between two regions with different danger assessments (e.g. different danger levels or different distributions of avalanche prone locations) but instead transitional areas which in many cases cannot be clearly assigned to either avalanche situation. This means that in a marginal area several kilometres wide, it can be assumed that both the more and the less favourite situations may apply.
Those undertaking backcountry ski or snowshoe hiking tours in such areas should therefore consult the avalanche bulletin for both regions in question.
Warning regions (the 138 smallest units)
Northern and southern flanks of the Alps, and the Jura
Main Alpine Ridge, Northern Alpine Ridge and Inneralpine Regions
The Main Alpine Ridge extends from Val Ferret via the Great St Bernard, Monte Rosa, Simplon, Gotthard, Lukmanier, San Bernardino, Maloja and Bernina passes to beyond Val Müstair.
The Northern Alpine Ridge covers a belt running from the Dent du Midi via the Wildstrubel and Jungfrau regions and Gotthard, Tödi and Vorab to Liechtenstein.
The Inneralpine Regions encompass the regions between the Main Alpine Ridge and the Northern Alpine Ridge, namely those of Central Valais, and parts of Northern and Central Grisons and Engadine.