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Avalanche bulletin through Monday, 22 April 2019
In the early morning a favourable avalanche situation will prevail. Wet avalanches as the day progresses
Edition: Su. 21.04., 17:00 Next update: Mo. 22.04., 17:00 Validity
Avalanche bulletin through Monday, 22 April 2019
In the early morning a favourable avalanche situation will prevail. Wet avalanches as the day progresses
Edition Su. 21.04., 17:00 Next update Mo. 22.04., 18:00 Validity
Avalanche bulletin through Monday, 22 April 2019
In the early morning a favourable avalanche situation will prevail. Wet avalanches as the day progresses
Edition Su. 21.04., 17:00 Next update Mo. 22.04., 17:00 Validity
Avalanche bulletin through Monday, 22 April 2019
In the early morning a favourable avalanche situation will prevail. Wet avalanches as the day progresses
Edition Su. 21.04., 17:00 Next update Mo. 22.04., 17:00 Validity
Level 1, low
Dry avalanches:
Individual avalanche prone locations for dry avalanches are to be found especially on extremely steep north facing slopes above approximately 2400 m. As a consequence of a strengthening southerly wind, mostly small wind slabs will form in particular above approximately 2600 m. Apart from the danger of being buried, restraint should be exercised in particular in view of the danger of avalanches sweeping people along and giving rise to falls.
Wet avalanches as day progresses
Level 2, moderate
Wet avalanches as day progresses
As a consequence of warming during the day, the likelihood of wet and gliding avalanches being released will increase. Medium-sized and, in isolated cases, large avalanches are possible. This applies on very steep south facing slopes below approximately 3400 m as well as on north facing slopes below approximately 2600 m. On very steep east and west facing slopes the avalanche prone locations are to be found below approximately 3000 m.
Backcountry tours and off-piste skiing should be concluded timely.
Dry avalanches
In the early morning a favourable avalanche situation will prevail. Wet avalanches as the day progresses
Edition: 21.4.2019, 17:00 / Next update: 22.4.2019, 18:00
Snowpack
The snow cover is favourably structured for the most part and, during the morning hours, stable.
The snowpack is becoming thoroughly wet to an ever greater degree. North-facing slopes are thoroughly wet up to approximately 2400 m, south-facing slopes up as high as high alpine regions, east-facing and west-facing slopes up to approximately 2800 m. What is currently most critical are the altitude bands and aspects which have become moist for the first time, that is, north-facing slopes between 2200 and 2600 m, and east and west-facing slopes between 2600 and 3000 m. In those regions, increasingly frequent area-wide, moist slab avalanches have been registered. During the nightttime hours, a crust forms on the snowpack surface. As a consequence of the reduced nocturnal outgoing (longwave) radiation, the crust at intermediate altitudes is hardly capable of bearing loads. The melt-freeze crust then softens and melts during the course of the day and the danger of wet-snow avalanches increases. However, due to dense cloud cover, it no longer melts to the same degree as in the last few days. On north-facing slopes on the northern flank of the Alps and in northern Grisons above 1000 m to 1400 m, in the other regions of Switzerland above 1400 m to 1800 m, there is a cohesive, area-wide snowpack. On south-facing slopes the snow levels lie approximately 400 m higher up.
The snowpack is becoming thoroughly wet to an ever greater degree. North-facing slopes are thoroughly wet up to approximately 2400 m, south-facing slopes up as high as high alpine regions, east-facing and west-facing slopes up to approximately 2800 m. What is currently most critical are the altitude bands and aspects which have become moist for the first time, that is, north-facing slopes between 2200 and 2600 m, and east and west-facing slopes between 2600 and 3000 m. In those regions, increasingly frequent area-wide, moist slab avalanches have been registered. During the nightttime hours, a crust forms on the snowpack surface. As a consequence of the reduced nocturnal outgoing (longwave) radiation, the crust at intermediate altitudes is hardly capable of bearing loads. The melt-freeze crust then softens and melts during the course of the day and the danger of wet-snow avalanches increases. However, due to dense cloud cover, it no longer melts to the same degree as in the last few days. On north-facing slopes on the northern flank of the Alps and in northern Grisons above 1000 m to 1400 m, in the other regions of Switzerland above 1400 m to 1800 m, there is a cohesive, area-wide snowpack. On south-facing slopes the snow levels lie approximately 400 m higher up.
Observed weather on Sunday, 21.04.2019
During the night, high-altitude cloud cover moved in from the south, which tended to reduce the outgoing radiation somewhat.
During the daytime, it was only partly sunny as a consequence of the intermittently heavy cloud cover in western regions more
than anywhere else.
Fresh snow
-
Temperature
At midday at 2000 m, betweeen +8 °C in the western regions and +6 °C in the eastern regions.
Wind
Winds were southeasterly,
- on the northern Alpine Ridge blowing at moderate to strong velocity,
-
in the other regions of Switzerland, blowing at light to moderate strength.
Weather forecast through Monday, 22.04.2019
Nighttime skies in the Valais will be predominantly overcast, in the other regions variably cloudy. During the daytime it
will be partly sunny accompanied by heavy cloud cover in some regions and intermediate altitude clouds. The clouds will tend
to become heavier in the afternoon in the western and the southern regions more than anywhere else. Nevertheless, it is expected
to remain predominantly dry until evening.
Fresh snow
-
Temperature
At midday at 2000 m, between +8 °C in the northern regions and +5 °C in the southern regions.
Wind
Winds will be southerly,
- blowing predominantly at moderate strength,
-
blowing at strong velocity on the northern Alpine Ridge, extending down to low lying areas in the foehn-exposed Alpine valleys.
Outlook through Wednesday, 24.04.2019
On the Main Alpine Ridge and southwards therefrom, skies will be heavily overcast and repeated bouts of precipitation are
anticipated. The snowfall level will lie at approximately 2000 m. The southerly winds will be blowing at strong velocity,
on Wednesday even reaching storm strength. In the northern regions, foehn wind will extend down to low lying areas.
By Wednesday evening in the Upper Valais section of the Main Alpine Ridge and on the southern flank of the Alps above approximately 2500 m, 40 to 60 cm of fresh snow is anticipated; in the Monte Rosa region even more. The danger of dry-snow avalanches will increase significantly at high altitudes in those regions. In the northern regions, a small amount of fresh snow is possible in high alpine regions more than anywhere else. The danger of wet-snow avalanches is not expected to change significantly.
By Wednesday evening in the Upper Valais section of the Main Alpine Ridge and on the southern flank of the Alps above approximately 2500 m, 40 to 60 cm of fresh snow is anticipated; in the Monte Rosa region even more. The danger of dry-snow avalanches will increase significantly at high altitudes in those regions. In the northern regions, a small amount of fresh snow is possible in high alpine regions more than anywhere else. The danger of wet-snow avalanches is not expected to change significantly.
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 early morning a favourable avalanche situation will prevail. Wet avalanches as the day progresses
Edition: 21.4.2019, 17:00 / Next update: 22.4.2019, 18:00
Snowpack
The snow cover is favourably structured for the most part and, during the morning hours, stable.
The snowpack is becoming thoroughly wet to an ever greater degree. North-facing slopes are thoroughly wet up to approximately 2400 m, south-facing slopes up as high as high alpine regions, east-facing and west-facing slopes up to approximately 2800 m. What is currently most critical are the altitude bands and aspects which have become moist for the first time, that is, north-facing slopes between 2200 and 2600 m, and east and west-facing slopes between 2600 and 3000 m. In those regions, increasingly frequent area-wide, moist slab avalanches have been registered. During the nightttime hours, a crust forms on the snowpack surface. As a consequence of the reduced nocturnal outgoing (longwave) radiation, the crust at intermediate altitudes is hardly capable of bearing loads. The melt-freeze crust then softens and melts during the course of the day and the danger of wet-snow avalanches increases. However, due to dense cloud cover, it no longer melts to the same degree as in the last few days. On north-facing slopes on the northern flank of the Alps and in northern Grisons above 1000 m to 1400 m, in the other regions of Switzerland above 1400 m to 1800 m, there is a cohesive, area-wide snowpack. On south-facing slopes the snow levels lie approximately 400 m higher up.
The snowpack is becoming thoroughly wet to an ever greater degree. North-facing slopes are thoroughly wet up to approximately 2400 m, south-facing slopes up as high as high alpine regions, east-facing and west-facing slopes up to approximately 2800 m. What is currently most critical are the altitude bands and aspects which have become moist for the first time, that is, north-facing slopes between 2200 and 2600 m, and east and west-facing slopes between 2600 and 3000 m. In those regions, increasingly frequent area-wide, moist slab avalanches have been registered. During the nightttime hours, a crust forms on the snowpack surface. As a consequence of the reduced nocturnal outgoing (longwave) radiation, the crust at intermediate altitudes is hardly capable of bearing loads. The melt-freeze crust then softens and melts during the course of the day and the danger of wet-snow avalanches increases. However, due to dense cloud cover, it no longer melts to the same degree as in the last few days. On north-facing slopes on the northern flank of the Alps and in northern Grisons above 1000 m to 1400 m, in the other regions of Switzerland above 1400 m to 1800 m, there is a cohesive, area-wide snowpack. On south-facing slopes the snow levels lie approximately 400 m higher up.
Observed weather on Sunday, 21.04.2019
During the night, high-altitude cloud cover moved in from the south, which tended to reduce the outgoing radiation somewhat.
During the daytime, it was only partly sunny as a consequence of the intermittently heavy cloud cover in western regions more
than anywhere else.
Fresh snow
-
Temperature
At midday at 2000 m, betweeen +8 °C in the western regions and +6 °C in the eastern regions.
Wind
Winds were southeasterly,
- on the northern Alpine Ridge blowing at moderate to strong velocity,
-
in the other regions of Switzerland, blowing at light to moderate strength.
Weather forecast through Monday, 22.04.2019
Nighttime skies in the Valais will be predominantly overcast, in the other regions variably cloudy. During the daytime it
will be partly sunny accompanied by heavy cloud cover in some regions and intermediate altitude clouds. The clouds will tend
to become heavier in the afternoon in the western and the southern regions more than anywhere else. Nevertheless, it is expected
to remain predominantly dry until evening.
Fresh snow
-
Temperature
At midday at 2000 m, between +8 °C in the northern regions and +5 °C in the southern regions.
Wind
Winds will be southerly,
- blowing predominantly at moderate strength,
-
blowing at strong velocity on the northern Alpine Ridge, extending down to low lying areas in the foehn-exposed Alpine valleys.
Outlook through Wednesday, 24.04.2019
On the Main Alpine Ridge and southwards therefrom, skies will be heavily overcast and repeated bouts of precipitation are
anticipated. The snowfall level will lie at approximately 2000 m. The southerly winds will be blowing at strong velocity,
on Wednesday even reaching storm strength. In the northern regions, foehn wind will extend down to low lying areas.
By Wednesday evening in the Upper Valais section of the Main Alpine Ridge and on the southern flank of the Alps above approximately 2500 m, 40 to 60 cm of fresh snow is anticipated; in the Monte Rosa region even more. The danger of dry-snow avalanches will increase significantly at high altitudes in those regions. In the northern regions, a small amount of fresh snow is possible in high alpine regions more than anywhere else. The danger of wet-snow avalanches is not expected to change significantly.
By Wednesday evening in the Upper Valais section of the Main Alpine Ridge and on the southern flank of the Alps above approximately 2500 m, 40 to 60 cm of fresh snow is anticipated; in the Monte Rosa region even more. The danger of dry-snow avalanches will increase significantly at high altitudes in those regions. In the northern regions, a small amount of fresh snow is possible in high alpine regions more than anywhere else. The danger of wet-snow avalanches is not expected to change significantly.
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)