Avalanche Bulletins and other products

Transcription

WSL Institute for Snow and Avalanche Research SLF
WSL-Institut für Schnee- und Lawinenforschung SLF
WSL Institut pour l'étude de la neige et des avalanches SLF
WSL Istituto per lo studio della neve e delle valanghe SLF
Avalanche Bulletins and other products
Interpretation Guide
Edition 2015
Responsible for the publication:
Dr. Jürg Schweizer
Head of the research unit avalanches and prevention, SLF Davos
Technical editing:
Avalanche Service / Thomas Stucki
Translation
TTN tele.translator.network
18, bd des Philosophes, CH-1205 Geneva, Switzerland
www.ttn.ch
Acknowledgements:
WSL Institute for Snow and Avalanche Research SLF (Publisher) 2015: Avalanche Bulletins and other
products. Interpretation Guide. Edition 2015. 16th revised edition. WSL Institute for Snow and Avalanche
Research SLF. 50 pages.
This edition replaces the 13th revised edition of 2012.
Also available in German, French and Italian
Orders (published only online):
http://www.slf.ch/schneeinfo/zusatzinfos/interpretationshilfe/interpretationshilfe_e.pdf
Photo:
Powder avalanche
Photo credit: J. Rocco
Avalanche bulletin and other SLF products
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Contents
1. Introduction .....................................................................................................................................5
2. What is an avalanche bulletin? ........................................................................................................5
3. Target audience ...............................................................................................................................6
4. Issuing office, publication frequency and validity ..........................................................................6
4.1 Issuing office ............................................................................................................................................................................... 6
4.2 Publication frequency and validity .............................................................................................................................................. 7
5. Resources used to produce the avalanche bulletin ..........................................................................8
6. Avalanche bulletin content and formats ..........................................................................................9
6.1 Content of the avalanche bulletin ................................................................................................................................................ 9
6.2 The interactive avalanche bulletin on the internet and in the app (iPhone and Android) .......................................................... 11
6.3 Avalanche bulletins for printing ................................................................................................................................................ 11
6.5 Icon map .................................................................................................................................................................................... 13
7. Capabilities and limitations of the avalanche bulletin ..................................................................13
8. Avalanche danger terminology .....................................................................................................14
8.1 Definition of avalanche danger ................................................................................................................................................. 14
8.2 Avalanche danger levels ............................................................................................................................................................ 14
8.3 The European avalanche danger scale ....................................................................................................................................... 15
9. Explanation of danger levels .........................................................................................................17
9.1 General ...................................................................................................................................................................................... 17
9.2 Low avalanche danger (level 1): ............................................................................................................................................... 18
9.3 Moderate avalanche danger (level 2)......................................................................................................................................... 18
9.4 Considerable avalanche danger (level 3) ................................................................................................................................... 19
9.5 High avalanche danger (level 4) ................................................................................................................................................ 19
9.6 Very high avalanche danger (level 5) ........................................................................................................................................ 19
10. Explanation of avalanche prone locations ...................................................................................20
10.1 General .................................................................................................................................................................................... 20
10.2 Slope angle .............................................................................................................................................................................. 20
10.3 Slope aspect............................................................................................................................................................................. 20
10.4 Altitude zone ........................................................................................................................................................................... 21
10.5 Other terminology describing especially critical terrain features ............................................................................................ 21
10.6 Use of terms in the avalanche bulletin..................................................................................................................................... 21
10.7 Graphic depiction of especially critical areas in the danger map............................................................................................. 22
11. Additional information and recommendations for individual user groups .................................24
11.1 General .................................................................................................................................................................................... 24
11.2 Permanent recommendations................................................................................................................................................... 24
11.3 Current recommendations ....................................................................................................................................................... 24
12. Geographical terminology ...........................................................................................................25
13. Supporting products ....................................................................................................................25
13.1 New snow maps ...................................................................................................................................................................... 25
13.2 Snow depth map ...................................................................................................................................................................... 26
13.3 Snow depth at 2000 m or 2500 m ............................................................................................................................................ 26
13.4 Snow depth compared with long-term mean ........................................................................................................................... 26
13.5 Snowpack stability map........................................................................................................................................................... 26
13.6 Weekly report .......................................................................................................................................................................... 27
13.7. Icons ....................................................................................................................................................................................... 27
14. Distribution channels and how to consult the products ...............................................................28
15. Feedback on avalanche danger ....................................................................................................29
16. Closing remarks ...........................................................................................................................29
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Appendix 1:
Appendix 2:
Appendix 3:
Appendix 4:
Appendix 5.1:
Appendix 5.2:
Appendix 5.3:
Appendix 6:
Appendix 7:
Appendix 8:
Appendix 9:
Appendix 10:
Appendix 11:
Appendix 12:
A ppendix 13:
Appendix 14:
Appendix 15:
Appendix 16:
Appendix 17:
Appendix 18:
Appendix 19:
Appendix 20:
European danger scale with recommendations ........................................... 32
Overview of European avalanche danger scales ......................................... 33
Specimen avalanche bulletin on the internet –
danger map including danger description ................................................... 34
Specimen avalanche bulletin on the internet – snowpack and weather ...... 35
Specimen full avalanche bulletin (for printing) .......................................... 36
Specimen full avalanche bulletin (for printing) .......................................... 37
Specimen regional danger map (for printing) ............................................. 38
Specimen icon map ..................................................................................... 39
SLF network of observer stations ............................................................... 40
IMIS (and SwissMetNet) stations (snow stations)...................................... 40
Geographical terminology V - the smallest units the 123 warning regions .............................................................................. 41
Geographical terminology I - northern and southern flank of the Alps ...... 42
Geographical terminology II - major political regions ............................... 42
Geographical terminology III - political subregions 1 ................................ 43
Geographical terminology IV - political subregions 2 ............................... 43
Geographical terminology VI: Main Alpine Ridge, northern
Alpine Ridge and inneralpine regions......................................................... 44
Specimen new snow map (1 day) ............................................................... 44
Specimen snow depth map.......................................................................... 45
Specimen snow depth map for 2000 m ....................................................... 45
Specimen snow depth map showing comparison with long-term mean
values .......................................................................................................... 46
Specimen snowpack stability map .............................................................. 46
Typical danger situations (avalanche problems)......................................... 47
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1. Introduction
The WSL Institute for Snow and Avalanche Research SLF has been publishing avalanche bulletins
since 1945. The Interpretation Guide was first published in 1985. It describes the avalanche
bulletin and additional products, and seeks to help the user interpret their contents. Changes were
incorporated in later editions (1993, 1994, 1998, 1999, 2001, 2002, 2003, 2004, 2007, 2008) to
reflect both new formats and publication times for the avalanche bulletin and the availability of
various supporting products. The preceding, thoroughly revised 2012 edition was issued in
connection with a fundamental overhaul of the avalanche bulletin. Only minor amendments were
made in the current 2015 edition. The basis of all the avalanche warnings issued by the SLF is the
standardised avalanche danger scale with five danger levels, which has been in use throughout
Europe since the winter of 1993/94. This scale, with minor deviations, is also acknowledged as the
norm overseas, in particular in Canada and the U.S.
The Interpretation Guide does not encompass the information platforms for the safety services,
such as the GIN (Joint Information Platform for Natural Hazards) and the IFKIS-InfoManager
(inter-cantonal early warning and crisis information system), or the special products they contain
which are not intended for the general public.
The users of these platforms receive training by attending courses for safety authorities at the SLF
(for details, see www.slf.ch/dienstleistungen/events/index_EN). The binding version of the
Interpretation Guide is always the most recently revised edition, which is made available on the
website of the SLF at www.slf.ch.
The descriptive terms for persons, job titles and professions in this Interpretation Guide refer to
both sexes unless otherwise indicated by the text.
The term "skier" in the context of avalanches, as in "skier(-triggered) avalanche", is widely used to
refer not only to skiers, but to all those who engage in snow sports, including snowboarders,
snowshoe hikers and others. It is used in this way in the Interpretation Guide as well.
2. What is an avalanche bulletin?
By way of the avalanche bulletin (and other supporting products), the WSL Institute for Snow and
Avalanche Research SLF informs the public about the current snow and avalanche situation in the
Swiss Alps. The content of the avalanche bulletin serves as a warning. The bulletin is published
twice daily during the peak winter season and primarily contains a forecast of the avalanche danger
in the Swiss Alps, Liechtenstein and, whenever necessary, the Jura as well. It also contains
information on the weather parameters that affect avalanches and on the quality of the snowpack.
The information provided by the avalanche bulletin serves as a basis for the user's own evaluation.
It does not replace an autonomous assessment of the situation in each given locality. The
information contained in the bulletin is too general for local assessment purposes because of the
limited data resources.
During the peak season, the structure of the avalanche bulletin remains unchanged. The structure of
the bulletin reflects the "information pyramid" illustrated in Figure 1. The most important topic (the
danger level) is at the top of the information pyramid, followed by the avalanche prone locations
(core zone), avalanche problems, a description of the danger, and information concerning the
snowpack and the weather. Finally, the data captured by the measuring stations can be displayed.
The use of standardised terminology aids both understanding and the practical interpretation of the
bulletin's contents.
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Fig. 1: The most important topic of the avalanche bulletin appears at the top of the information pyramid. Further
down the pyramid, the amount of detail contained in the information gradually increases.
3. Target audience
The avalanche bulletin is intended for all those who are exposed to potential avalanche danger in
the mountains in winter, whether engaging in a professional or recreational activity, including those
who are responsible for the safety of others. This includes members of the following groups:
•
Avalanche services and committees of the district authorities and civil engineering
offices, as well as the safety services of the mountain railway and cableway
operators
•
Police and rescue services and the armed forces
•
Mountain guides, snow sport instructors and backcountry tour guides
•
Residents of mountain villages
•
Skiers and snowboarders
•
Backcountry skiers, snowshoe hikers
•
Mountaineers and ice climbers
•
Other snow sport participants
The long-term (20-year) annual average number of avalanche victims in Switzerland is 23.
Accident analyses show that most avalanche victims come to grief in open terrain; that is to say,
while engaging in leisure activities on skis, snowboarding, or taking part in mountain climbing or
similar pursuits. This group's share of fatalities between 2002/03 and 2011/12 was more than 90%.
Of these victims, about 90% triggered the avalanche themselves or it was released by another
member of the same group.
When the snow and avalanche situation is relatively stable, the pointers for backcountry skiers, for
example, are more elaborate than those for the local avalanche authorities. From danger level 3
(considerable avalanche danger), more recommendations are issued for the avalanche safety
services. In particular when the avalanche danger is high (level 5) and snow sport activities in open
terrain are thus extremely restricted, the recommendations for the avalanche safety services are
even more extensive.
4. Issuing office, publication frequency and validity
4.1 Issuing office
The editorial office of the Swiss avalanche bulletin is attached to the WSL Institute for Snow and
Avalanche Research SLF in Davos. The avalanche warning service is the responsible body.
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4.2 Publication frequency and validity
The avalanche warning service monitors the weather, snow and avalanche situation throughout the
year. The frequency of publication and contents of the avalanche bulletin vary according to the
seasonal conditions.
4.2.1 Winter
In the winter, the avalanche bulletin consists of two parts, as described below.
1. Danger map including danger description:
This part of the avalanche bulletin is issued twice daily in four languages (German, French, Italian,
English). The 5 pm edition forecasts the avalanche danger for the next 24 hours – until 5 pm the
next day.
The danger is reassessed in the mornings at 8 am, also in four languages (German, French, Italian,
English). This forecast is valid until 5 pm.
In principle, a further assessment of the avalanche danger can be issued at any time, but this option
is used only seldom.
2. Information on the snowpack and weather:
This part of the avalanche bulletin is produced only in the evenings. It is published at 5 pm in
German and around 6.00 pm in French, Italian and English, and is valid until 5 pm or 6.00 pm the
next day.
4.2.2 Early and late winter season
As a general rule, an avalanche bulletin together with a danger map continues to be published for
as long as the data resources (cf. Chapter 5) allow a detailed assessment of the danger, including
the danger levels. In the transitional periods between autumn and winter (typically from the end of
October until early December) and between spring and summer (typically from the end of April
until early June), the avalanche bulletin is published only in the evenings. The format and content
are the same as in the winter. The bulletin may cover a period of several days, running until 5 pm
on the indicated final day of validity.
The issue of bulletins with a danger map and the frequency of publication depend on the following
factors in particular:
•
Information density: The SLF observers work every day from November 1 to April 30.
Outside this period, fewer observations take place in the field. One reason for this reduction
is the generally low level of snow sport activity. When direct observation is not taking place,
information is obtained mostly by telephone as required and available. In some cases,
observers cannot return to work until after November 1, once the mountain railway and
cableway services are resumed. Likewise, their annual duty can end before April 30. In
contrast, access to the network of automatic measuring stations is available during the
summer as well.
•
Demand: Favourable snow conditions in large parts of the Swiss Alps and the seasonal
reopening of the mountain railways and cableways increase the demand for daily avalanche
bulletins.
4.2.3 Summer and autumn
From early summer until late autumn, avalanche bulletins are published in text form and generally
without reference to danger levels only in the event of heavy snowfall. In the late autumn, bulletins
are issued according to the snow situation and availability of information. These bulletins are
published at 5 pm in German and around 6.00 pm in French, Italian and English, and are valid for
one or several days, running until 5 pm on the indicated final day of validity.
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The criteria for publishing an avalanche bulletin are satisfied if the forecast amount of new snow
per precipitation event (normally 1 to 3 days) reaches one of the following values:
• 20 cm at 2000 m or
• 40 cm at 2500 m or
• 60 cm at 3000 mm or
• 80 cm at 3500 m
The indicated values are not exact, but only guidelines. They can vary, depending on the wind,
temperature and the extent and properties of the existing snowpack. The snowfall event must affect
at least an entire massif. Local snowfall, such as occurs when triggered by individual thunderstorm
cells, is disregarded.
4.2.4 Special case of Jura (and Sotto Ceneri)
The situation that prevails in Jura differs from that in the Alps insofar as an elevated avalanche
danger occurs only on a few days and in a few places. When such a danger arises, however, it is not
to be underestimated. For this reason, the daily avalanche bulletin indicates a danger level for the
Jura only if the danger is categorised as considerable (level 3) or higher. A danger of the relevant
magnitude occurs on around five days throughout the winter. All five danger levels are published
for Sotto Ceneri. When there is no (more) snow lying on the ground, the indication of a danger
level is omitted.
5. Resources used to produce the avalanche bulletin
The avalanche warning service uses a variety of resources to compose the avalanche bulletin:
•
About 180 observers with an array of measuring programmes (measurement, observation,
evaluation) file reports between 6 and 8 am in the morning or sometimes in the middle of
the day
•
Around 100 automatic measuring stations (intercantonal measurement and information
system (IMIS)), and the data collected by about 80 SwissMetNet stations (automatic
measuring network) operated by the Swiss meteorological office, MeteoSwiss
•
Every two weeks, about 40 flat-field and slope profiles with stability tests
•
Forecasting products of MeteoSwiss and other weather services
•
Reports of actual avalanches, filed by backcountry skiers and others (cf. Chapter 15)
•
Feedback to assist the assessment of the avalanche danger, provided by backcountry skiers
and others (cf. Chapter 15)
Four of the typical observer groups are observer stations, regional observers, mAvalanche
observers, and measuring station observers. The observers at the observer stations (cf. Appendix
7) record the key weather conditions (including precipitation and cloud) and, in a specific sampling
area, the snow characteristics (new snow, overall snow depth, penetration depth, new snow density,
surface structure), while the regional observers assess similar variables within their territory
without a specific sampling area. In addition, members of both groups report their own
observations (e.g. released avalanches, alarm signs), as well as their assessment of the avalanche
danger. mAvalanche observers are mountain guides who report their observations and
assessments, made en route with tourists, to the avalanche warning service by 3 pm. They file and
transmit their reports by way of an app. They focus in particular on observations concerning new
snow, alarm signs etc., and on a current assessment of the avalanche danger. Unlike the members
of the other groups, these observers move freely within the territory of the Swiss Alps. Only the
new snow and the snow depth are measured at the measuring stations. These measurements serve
climatological and hydrological purposes in particular (long-term serial studies). For the
operational snow-hydrological service, fresh fallen snow, snow depth and water content of the
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entire snowpack is measured at certain stations during summertime as well, but only in direct
response to relevant weather-based events.
The observers are located throughout the entire Swiss Alps. Their measuring and observation posts
are situated mostly at altitudes of 1000 to 2700 m. The avalanche observers in particular also reach
higher altitudes, and some measuring stations exist at lower altitudes.
The hourly and half-hourly measurements of the various automatic snow measuring stations in the
IMIS network established in collaboration with the responsible agencies of the mountainous
cantons, as well as the automatic SwissMetNet stations of MeteoSwiss, have also proven very
useful in the assessment of the avalanche danger (for a map of the SwissMetNet/IMIS stations, see
Appendix 8).
Alongside the data that are collected daily, another key resource is the approximately 40 slope and
flat-field profiles that are taken every 14 days throughout the Swiss Alps. These profiles are
produced by observers either at the flat test sites or, in the case of slope profiles, on representative
test slopes in conjunction with rutschblock tests.
A variety of forecasting products of MeteoSwiss and the European Centre for Medium-Range
Weather Forecasts, as well as other providers' aids as necessary, are used to evaluate the short-term
weather prospects.
To facilitate a better assessment in the border regions, information is regularly exchanged with the
neighbouring countries' avalanche warning services (www.lawinen.org).
6. Avalanche bulletin content and formats
The avalanche bulletin has been optimised for the principal distribution channels, namely the
internet and smartphones. Various versions suitable for printing are also made available.
The "flash" and "avalanche danger" sections are compiled from a catalogue of standard phrases and
produced simultaneously in all the languages. This content can therefore be published in all the
languages in the mornings as well.
6.1 Content of the avalanche bulletin
The content of the winter avalanche bulletin is described below. The summer bulletins are
explained in Chapter 6.4.
6.1.1 Flash
The flash section is a very brief pointer to the key aspects of the avalanche situation.
6.1.2 Avalanche danger
The description of the avalanche danger is the most important part of the avalanche bulletin. It
contains the forecast for the relevant period. Regions that are subject to the same danger level and
in which similar areas are especially critical (core zone, cf. Chapter 10.6) are grouped together.
Regions subject to the same danger level are treated separately if the core zone is not identical (e.g.
different altitude zone or aspect). The avalanche danger can be described in even greater detail with
phrases such as "danger of dry avalanches", "danger of wet avalanches as the day progresses", or
"danger of gliding avalanches". The description of the avalanche danger contains the following
elements:
• Danger level
The danger level is described with reference to the five-point European avalanche danger
scale (cf. Appendix 1): low (level 1), moderate (level 2), considerable (level 3), high (level
4), and very high (level 5).
• Avalanche prone locations (core zone)
9
•
•
•
•
In most cases, the especially critical locations – the areas that are exposed to especially
significant danger – are depicted graphically (in the danger map as well) and described in
plain text. More detailed information on avalanche prone locations is contained in Chapter
10.
Avalanche problems (cf. Appendix 20)
The words used to describe the avalanche situation denote one or more typical "avalanche
problems" – crucial conditions governing the release of an avalanche. This general
approach draws attention to the main problem. The avalanche bulletin highlights the
following problems:
- New snow
- Snow drifts (snow transported by the wind)
- Old snow (e.g. "fractures in the old snowpack")
- Wet snow, in which case a distinction is made between:
- wet avalanches
- wet avalanches as the day progresses
- gliding avalanches
- favorable situation (now other problem, level 1 (low))
Danger description
This section gives a fuller description of the danger illustrated by the danger map. Among
other aspects, it can describe the likelihood and size of the anticipated avalanches, and the
snowpack structure typically indicating the location of weak layers in the snowpack. As
necessary, this section also contains special remarks (cf. Chapter 11) for the different user
groups.
Additional danger
If necessary, the description of the main danger can be followed by the indication of an
additional danger as well. If both dry and wet avalanches are expected, for example, the
relevant information is provided here. If wet avalanches are the main source of danger,
however, this is the danger that is highlighted in both the danger map and the danger
description. In such an event, the danger of dry avalanches, for example, can be mentioned
under the "additional danger" heading. Apart from the absence of a graphic depiction of the
especially critical locations, the description of the additional danger adopts the same format
as the text outlining the main danger. If two maps are published (cf. Chapter 9), only the
main danger is described in each of the maps.
Remarks
This section provides an opportunity to present users with more information, typically
concerning an additional source of danger or an especially uncertain development.
6.1.3 Snowpack and weather, outlook
The snowpack is the principal determining factor in the formation of avalanches. The snowpack
section describes the properties of the snowpack that characterise the current situation. The
description is general and usually covers both the structure and the stability of the snowpack. The
snowpack structure is determined by the layering and structural properties of its individual layers
(grain shape and size, hardness). The snowpack stability is a measure of the ease with which
avalanches can be triggered or naturally released. The snowpack structure determines its stability.
This section also describes the observed avalanche activity if applicable.
The weather directly and significantly influences the snowpack and therefore the development of
the avalanche danger. The weather section describes the key factors that exert an influence on the
development of the avalanche danger. These are typically new snow (or rain), air temperature,
wind, and the cloud conditions. The description begins with a review of the weather conditions in
the immediately preceding period (covering at least the current day), which is followed by the
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forecast for the validity period of the avalanche bulletin. The danger assessment is formulated on
the basis of this weather forecast. If the actual weather pattern differs from the forecast, the
anticipated avalanche danger may also be inaccurate.
Based on the medium-term weather forecast, the outlook assesses the general pattern of the
avalanche danger for the two days immediately following the bulletin's validity period.
6.2 The interactive avalanche bulletin on the internet and in the app (iPhone and Android)
The interactive bulletin operates in a broadly similar way on the internet and in the app, so that the
description below applies to both media (notes applying only to the app are enclosed in brackets).
6.2.1 Header
The header indicates the validity period (date, time of current and next update) and contains the
flash.
6.2.2 Interactive danger map
This map, which appears under the "Avalanche danger" tab, illustrates the assessed avalanche
danger for the Swiss Alps, Liechtenstein and, as necessary, the Jura as well. It indicates the danger
level and a graphic depiction of the aspect and altitude of the especially critical terrain. Navigation
is facilitated by the zoom function. By holding down the mouse button (swiping the phone display
with your finger), you can move the zoomed portion of the map.
The interactive danger map gives access to the danger descriptions: moving the mouse over
(tapping on) the map highlights the assessment for the currently selected location in full colour,
while all the other assessments are faded. Clicking on the map with the mouse (tapping on
"Details") displays in an additional window the full danger description for the relevant assessment
(danger level, avalanche prone locations (if applicable), danger description), the additional danger
(if applicable), and the remarks (if applicable).
The avalanche bulletin is issued with one or two danger maps. If two maps are provided (e.g. if the
avalanche danger is forecast to increase during the day), the actions described here have to be
performed twice – once for each map. At the end of each danger description, the user is made
aware of the other map. Danger maps for wet and gliding avalanches, and generally those depicting
a low avalanche danger (level 1), do not usually indicate the aspect and altitude.
6.2.3 Snowpack and weather
The "Snowpack and weather" tab gives access to the content described in Chapter 6.1.3. Since
around an hour is needed to translate the snowpack and weather information into French, Italian
and English after the danger map and description are published, the map is temporarily replaced by
a wildcard. By way of the archive, users can consult the information contained in the previous
avalanche bulletin if they wish.
6.2.4 Cross-link column
The blue cross-link column on the right of the webpage gives access to additional content,
supplementing and embellishing the information contained in the avalanche bulletin. Among other
items, the print products (cf. Chapter 6.3) are available here.
6.3 Avalanche bulletins for printing
Given that the interactive bulletin is not suitable for printing, a variety of print products are
produced as well:
• Danger map for Switzerland
• Individual danger regions, including danger description
• Snowpack and weather
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• Full avalanche bulletin
• Regional danger maps
The print products are compiled from the content of the interactive avalanche bulletin. All the print
products not only indicate the validity period and the time of the current and next update, but also
contain the flash. The individual products contain the following information:
6.3.1 Danger map
The danger map encompasses all of the regions for which a danger level has been issued, and a
graphic indication of the aspects and altitudes in which the danger is especially significant.
Clicking on "Individual danger regions" enables you to print the danger map for Switzerland with a
danger description for one danger region. If the avalanche bulletin consists of two danger maps,
each of the maps has to be printed separately.
The content concerning the snowpack and weather, as described in Chapter 6.1.3, can be printed
separately from the danger maps. In view of the delay for translation, the snowpack and weather
information in French, Italian and English is published a good hour later than the danger maps, at
around 6.00 pm.
6.3.3 Complete avalanche bulletin
This item enables you to print the whole bulletin, comprising the danger map for Switzerland, the
danger descriptions for all danger regions, and the information concerning the snowpack and
weather. In view of the delay for translating the snowpack and weather information, the complete
avalanche bulletin in French, Italian and English is published a good hour later than the danger
maps, at around 6.00 pm. In the mornings, the full avalanche bulletin is published in all the
languages at the same time, 8 am.
6.3.4 Regional danger map
The regional danger maps (cf. Appendix 5.3) replace the regional avalanche bulletins that were
published until winter 2011/12. They are suitable for displaying at freeride checkpoints near
cableways, for example. From a map, the user selects the relevant warning region (the smallest
territorial unit for avalanche reporting purposes). The print product contains the relevant regional
map for the selected territory (Bernese and Fribourg Alps, central part of the northern flank of the
Alps, eastern part of the northern flank of the Alps, Lower Valais and Vaud Alps, Upper Valais,
northern and central Grisons, Ticino and Moesa, Engadine and southern valleys, Jura), and the
danger description for the selected region is printed as well. The danger levels for the neighbouring
regions are also shown, but not described in any detail.
Those who regularly need a danger map for a particular territory (e.g. for a mountain refuge or ski
resort) can place a bookmark ( Instructions “Always select the same region“).
6.4 Avalanche bulletins in the summer and autumn
In the summer and autumn, avalanche bulletins are published according to the prevailing
conditions and without the danger map (cf. Chapter 4.2.3). Alongside the online version, the print
products are also issued in the summer. The bulletin may be valid for one or several days. The
validity period is stated in the bulletin, which comprises the following elements:
6.4.1 Header
The header not only indicates the validity period and the time of the current and next update, but
also contains a short title or flash.
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6.4.2 Avalanche danger
This section provides a general description of the avalanche situation. As a rule, danger levels are
not published in the summer because, in most cases, too little information is available for
assessment purposes.
The content under this heading largely corresponds to that described in Chapter 6.1.3, but the
information concerning the snowpack structure is less detailed than in the winter.
6.4.4 Outlook
The outlook is a brief description of the pattern of weather and avalanche danger for the two days
immediately following the bulletin's validity period.
6.4.5 Information
This section is intended for general information, such as a pointer to the "SLF Sommer" SMS
service (cf. Chapter 14).
6.5 Icon map
An icon map is produced to provide print media and websites with a much simplified overview of
the avalanche situation (Appendix 6). If the avalanche bulletin consists of two danger maps, the
icon map depicts the more severe danger. Such cases occur most frequently when typical
springtime conditions prevail – when the avalanche danger is generally higher in the afternoon.
7. Capabilities and limitations of the avalanche bulletin
As a general rule, the accuracy of both weather forecasting and the subsequent prognosis of the
avalanche danger can be compromised by inaccurate assessments. Such is the nature of forecasting.
The correlation that exists between the regional danger level, possible avalanche activity and
the relevant consequences (and any action that needs to be taken) must be determined locally
by the individual user of the avalanche bulletin. When the weather situation is changing rapidly,
it is impossible to describe the emerging spatial and temporal variations in the avalanche danger
accurately.
The bulletin uses only general formulations. It is unable to assess local conditions and certainly
not individual slopes. For this reason, snow sport participants and those responsible for safety
must rely on their own procedures when assessing the local situation. Such procedures include
local weather, snow and avalanche observations; snowpack analysis; examining maps; slope
evaluation in the field; and individual risk considerations. The safety services may also have access
to the results of artificial avalanche triggering. All the available information should be taken into
consideration before making a decision. Particular attention is to be paid to information indicating
unstable conditions.
The avalanche bulletin reports only on conditions outside the areas protected by the local railway
and cableway safety services. It does not cover controlled ski runs and pistes.
The avalanche bulletin may describe slopes or parts of slopes where especially critical conditions
are to be expected. In view of the available data resources, however, it is able to indicate only the
regional avalanche danger. Detailed information cannot be provided on small areas.
It is also worth noting that the information density is highest for intermediate and high altitudes,
and lowest for the high Alpine regions. Remarks concerning the high Alpine regions therefore
demand special scrutiny.
13
The SLF expressly reserves the right wholly or in part to revise, delete or temporarily not to
publish content at any time without notice.
8. Avalanche danger terminology
8.1 Definition of avalanche danger
Generally speaking, the word "danger" denotes the potential occurrence of a perilous process, such
as an earthquake, flash flood, debris flow or avalanche. This danger or perilous process is described
by indicating the likelihood of its occurrence and the anticipated magnitude of the event. The word
"danger" does not indicate whether the process will actually take place or, in an individual case,
give rise to material damage or physical injury. The actual occurrence of damage or injury depends
on whether any people or physical assets are situated within the reach of the "dangerous process"
(in this case, in the path of the avalanche) at the time it is triggered. In the context of the avalanche
bulletin, the term "avalanche danger" describes the likelihood of occurrence and the possible
size of avalanches in a specific region, but the exact moment of an avalanche's release and the
actual length of its starting zone and fracture depth cannot be precisely determined.
The word "risk", indicating potential damage or injury, presupposes the existence of both danger
and potentially endangered objects. Although avalanche bulletins describe the danger, and not the
risk of avalanches, the remarks below briefly highlight the difference.
If an avalanche occurs in an isolated, unwooded mountain valley where neither people nor physical
assets are situated, an avalanche danger, but no avalanche risk, exists there. If the avalanche
reaches a populated mountain valley, however, and thus endangers both people and property, not
only does an avalanche danger exist, but it can be accompanied by a high avalanche risk as well.
As a general rule, "avalanche danger" denotes the possible occurrence of a potentially damaging
avalanche. The likelihood of the event is the focal point. Whether, and the extent to which a risk
exists, depends on the locality and the way in which the people there behave. Avalanches are
peculiar and unlike flash floods or earthquakes inasmuch as the "perilous process" of an avalanche
can be initiated by human activity. If someone treads on an endangered slope, the artificial
additional load can significantly increase the existing natural likelihood of an avalanche (more than
90 percent of those buried by avalanches have triggered the event themselves).
8.2 Avalanche danger levels
Ever since the avalanche bulletin was first published in 1945, the avalanche danger has been
categorised with descriptions such as "the avalanche danger is high" or "the avalanche danger is
low at present". The extent of the avalanche danger depends on several factors, namely:
•
the snowpack stability, which is determined by the strength or bonding of the individual
layers and the likelihood of fracture propagation, among other things;
•
the triggering probability, which depends on the natural snowpack stability and can be
increased by human activity (snow sport participants, use of explosives etc.). The likelihood
of an avalanche being triggered (and therefore the avalanche danger) is low if the snowpack
stability is high. By the same token, the avalanche triggering probability is high if the
snowpack stability is low;
•
the surface spread and/or prevalence of critical slopes;
•
the size and type of the anticipated avalanches; in other words, the thickness of the sliding
snow layers (avalanche volume).
When the avalanche danger is being assessed, attention must therefore be paid to both the
triggering probability – the likely occurrence of a potentially perilous process – and the anticipated
extent of the avalanche. Wet snow slides with shallow fracture depths and originating from a rocky
14
south facing slope are generally less dangerous than a single, medium-sized, dry slab avalanche
with a slab thickness of one metre.
8.3 The European avalanche danger scale
8.3.1 Origination and development
In April 1993 the avalanche warning services of the Alpine countries agreed upon a uniform, fivepart European avalanche danger scale. Until then the individual countries had used various scales
with differing numbers of danger levels (e.g. 7 levels in Switzerland, 8 levels in France) and a
variety of definitions of the individual dangers. Since the adoption of a uniform scale, user groups
in all the countries have been able to refer to the same warning levels, which is of great benefit to
all snow sport participants visiting border areas or other countries.
In May 1994, once everyday experience had accumulated, further minor adjustments were made to
individual danger levels in the various languages. This gave rise to a uniform solution with
equivalent formulations paying due regard to the sensitivities of the different languages.
In an endeavour to make the information as precise as possible, the working party of the European
avalanche warning services more closely defined the most frequently used terms. These definitions
were approved at the meeting of the avalanche warning services in May 2003 and have been
subsequently revised according to need. Some of the definitions are explained in the following
chapter, and a separate glossary of the terms is published on the internet (www.avalanches.org).
8.3.2 Terminology
The first four columns of Appendix 1 (European avalanche danger scale with recommendations)
contain the danger scale that is currently valid throughout Europe. The standardised European
avalanche danger scale contains five ascending danger levels: low – moderate – considerable –
high – very high. These danger levels are described by reference to the snowpack stability and the
avalanche triggering probability, as well as the geographical extent of the avalanche prone
locations and the avalanche size and activity.
The snowpack stability is the ratio of snowpack strength to the existing stresses. The snowpack
stability forms the basis of all statements concerning the avalanche danger because it directly
controls the probability of an avalanche being released. Consideration is to be given to the
following factors as well:
•
The snowpack changes under the influence of the weather and metamorphism, so that its
stability varies too.
•
Although the snowpack is in any case variable to a greater or lesser extent, it also regularly
contains weak layers that not only extend over a large area which is key to avalanche
formation, but also determine the snowpack stability.
The assessment of snowpack stability therefore relies on extrapolation and forecasting methods,
such as the forenamed measurements taken in sampling areas, snow profiling, avalanche
observations, and snowpack stability tests.
In general, good snowpack stability – a strong, well-bonded snowpack – is associated with low
avalanche danger. A similar rule applies in reverse: low snowpack stability, in other words weak
bonding of the snow layers, indicates elevated avalanche danger.
In the interests of readability, the avalanche bulletin generally describes only the snowpack
stability of especially critical terrain features, so that statements on the altitude zone, aspect or type
of terrain are restricted to particularly dangerous areas.
The avalanche triggering probability is a measure of likelihood that depends directly on the
snowpack stability. The European avalanche danger scale explains the individual danger levels by
describing the relevant avalanche triggering probabilities. It indicates both the conditions that exist
in the absence of external influences (for natural avalanches) and the probability of avalanches
being released by additional loads (originating from snow sport participants, explosive charges
15
etc.). In particular, a distinction is made between high (large) and low (small) additional loads.
The loads described in Table 1 serve as examples of high and low additional loads:
Table 1: Additional loads
Low
additional load
High
additional load
•
•
•
•
•
Single skiers or snowboarders making gentle turns, not falling
Groups with spacing between individuals (at least 10 m during ascent, more
during descent)
Single snowshoe hikers
Two or more skiers or snowboarders without spacing (e.g. at a meeting
point or the location of a fall)
Snowmobile/groomer, avalanche blasting, ice debris from glaciers
These descriptions are to be regarded as guidelines and not used in isolation or afforded excessive
weight for evaluation purposes. The following points deserve special attention:
•
Avalanche danger does not depend solely on the triggering probability, but also on the
prevalence of avalanche prone locations.
•
The depth of the loosely bonded layers in the snowpack and the composition or quality of
the overlying snow layers are at least as important as the additional load. Furthermore, the
load exerted by a skier may differ from that exerted by a hiker. Whereas the skier exerts a
load on a larger area, the hiker sinks deeper into the snow. The effect of each type of load
can be more or less favourable, depending on the situation.
Table 2 describes the individual avalanche size categories (based on the Canadian avalanche size
classification) that are applied in the avalanche bulletin.
Table 2: Avalanche sizes
Classification/
size class
Potential damage classification
Runout classification
Typical length and volume
Relatively harmless to people,
unlikely to bury a person (except in
Stops within steep slope
unfavourable runout zones a danger
of falling exists in extreme terrain)
Approx. 10 – 30 m
100 m3
Could bury, injure or kill a person
Can reach the base of the slope
Approx. 50 – 200 m
1000 m3
Can traverse flat terrain (well below
Several hundred metres
30°) over a distance of less than
10,000 m3
50 m
Size
2
Sluff /
"rutsch"
(very small
avalanche)
Small
avalanche
Size
3
Medium
avalanche
Could bury and destroy cars,
damage trucks, destroy small
buildings and break a few trees
Size
4
Large
avalanche
Could bury and destroy trucks and Traverses flat terrain (well below
railway cars, and destroy fairly large 30°) over a distance of more than
buildings and small areas of forest 50 m, can reach the valley floor
Approx. 1 – 2 km
100,000 m3
Size
5
Very
large
avalanche
Could devastate the landscape, has
catastrophic destructive potential
Approx. 3 km
> 100,000 m3
Size
1
Reaches the valley floor, largest
known avalanche
According to this definition, typical skier avalanches fall within the category of small avalanches,
but they reach a considerable size as a general rule. Their average length is 150 metres and they
have a slab size of 50 by 80 metres, a mean slab thickness of around 50 m, and a cubature of about
2000 m³. These dimensions give rise to a mass of around 400 tonnes. In the event of high or very
high avalanche danger, large or very large avalanches can sometimes be released in isolated cases
even in moderately steep terrain, that is at slope angles of slightly less than 30 degrees.
16
The main purpose of this classification is to describe avalanche activity.
9. Explanation of danger levels
9.1 General
The avalanche danger expressed in the avalanche danger scale increases from level to level. At the
same time, the snowpack stability decreases (cf. Figure 2) and the prevalence of avalanche prone
locations in open terrain increases. Generally speaking, the additional load required to trigger an
avalanche decreases at the higher levels. The higher the danger level, the larger the avalanche size
and number of avalanches.
Fig. 2: Occurrence of stability categories with danger levels low (level 1) to considerable (level 3). As the danger
level increases, so does the proportion of areas where stability is weak. Also note the proportion of areas where the
stability is weak when the danger level is moderate (level 2).
The avalanche bulletin indicates any changes in the danger level that are expected to arise during
the day covered by the forecast. Examples:
•
"Danger level 3 (considerable) will not be reached until the afternoon."
•
"Danger level 4 (high) will already be reached during the morning."
•
"As the avalanche danger increases during the day, wet avalanches are to be expected again
from the middle of the day below approximately 2400 m."
The description of the avalanche danger can differ under the separate headings "danger
description" and "additional danger".
•
If the danger level is likely to change during the day, both the level published in the
avalanche bulletin and the danger description are guided by the situation in the morning.
The outlook (generally an increase in danger) is described under the heading "additional
danger".
•
Since most avalanches that cause damage and injury are dry slab avalanches, more space is
usually devoted to describing this danger in the avalanche bulletin.
•
In typical "springtime situations", that is on days when the avalanche danger increases
significantly during the day, two maps are used to depict both the more favourable morning
situation and the less favourable situation prompted by the increasing wet avalanche danger
as the day progresses (cf. Appendix 5).
If a substantial danger of gliding avalanches exists and this danger is greater, over a wide area, than
the danger of dry slab avalanches, two maps are produced to show both the danger of dry slab
17
avalanches and the danger of gliding avalanches. Note in this case that the danger of gliding
avalanches does not vary during the day. Both dry slab and gliding avalanches can therefore occur
at any time of day (including in the early morning).
The frequency of the published danger levels from winter 1997/98 to winter 2011/12 (serving as a
forecast for the following day since the avalanche bulletin was introduced) is depicted in Figure 3
below.
Fig. 3: Occurrence in percent of individual danger levels in the avalanche bulletin (evening assessment (5 pm) from
01.12. until 30.04.) from winter 1997/88 to 2011/12.
9.2 Low avalanche danger (level 1):
The snowpack is generally well bonded or, as a whole, loosely packed. Such conditions frequently
occur in mid-winter during long spells of fine weather accompanied by shallow snow cover. When
either one of these conditions prevails, a fracture is usually unable to propagate in the snowpack.
The snowpack is therefore generally stable (cf. Fig. 2). In isolated cases in extremely steep terrain,
avalanches can be triggered artificially by large additional loads (e.g. explosives or groups of
winter sport participants). Human-triggered avalanches can never be ruled out entirely. The
dangerous zones are sparse, however, and largely limited to extremely steep terrain. In extremely
steep terrain, the danger of avalanches sweeping people along and causing them to fall is often
greater than the danger of being buried.
Natural avalanches rarely occur, apart from small slides and small avalanches in steep terrain.
Around five percent of all fatal accidents occur at this danger level.
9.3 Moderate avalanche danger (level 2)
The snowpack is only moderately well bonded (cf. Fig. 2) in some places, as generally specified in
the avalanche bulletin by reference to the altitude zone, aspect or type of terrain. Provided that
routes are selected carefully, the conditions for snow sport activities are favourable in the majority
of cases.
If weak layers exist deep in the snowpack, medium-sized avalanches can be released in some
places in particular by large additional loads (cf. Chapter 8.3.2). Especially in places where the
snow cover is shallow, the possibility of an avalanche being released even by a small additional
load (cf. Chapter 8.3.2) cannot be ruled out. Such triggering occurs more frequently in connection
18
with new snow drift accumulations which, although released easily, are generally small. Alarm
signs, such as whumpfing sounds, can exist in isolated cases.
If natural avalanches occur, they are generally wet avalanches. In isolated cases, they can reach
medium size. Large natural avalanches are not to be expected. Transportation routes and
settlements are rarely exposed to the danger of natural avalanches. Safety measures are also
generally unnecessary on marked and open pistes.
Around one-third of all fatal accidents occur at this danger level.
9.4 Considerable avalanche danger (level 3)
On many slopes the snowpack structure is only moderate to weak (cf. Fig. 2). Triggering is
possible even with small additional loads (cf. Chapter 8.3.2), especially on the steep slopes in the
indicated aspects and altitude zones stated in the avalanche bulletin. Alarm signs typically exist,
but not in every case. Isolated slab avalanches can be released even from well outside the starting
zone (remote triggering).
The danger of natural avalanches can differ greatly. In case of a weakly bonded snowpack and
shallow snow cover, medium-sized avalanches are to be expected only sporadically. If this danger
level is forecast after new snow or in connection with (daytime) warming, isolated large avalanches
are possible as well. Safety measures, such as the use of explosives (especially in the case of new
snow) or temporary closures (especially if temperatures are expected to rise) of exposed parts of
transportation routes and, in particular, snow sport runs that are subject to protection by technical
measures, are to be recommended. Those engaging in backcountry touring and off-piste activities
must dispose over experience and assessment skills acquired through avalanche training. Steep
slopes in the indicated aspect and altitude zone are to be avoided as far as possible.
Around one-half of all fatal accidents occur at this danger level.
9.5 High avalanche danger (level 4)
The snowpack is weakly bonded on most slopes. Triggering is probable even by small additional
loads on numerous steep slopes. Alarm signs often exist. Natural avalanches and remote triggering
are typical. In certain cases, when the avalanches are not especially large, snow sport participants
are most endangered. Frequently, however, parts of transportation routes and settlements are
exposed to danger. Depending on the situation (e.g. snowpack structure, new snow, wind),
numerous medium-sized natural avalanches and a greater prevalence of large avalanches, which
generally follow familiar paths, are to be expected. Exposed parts of transportation routes and
settlements in the areas affected by such avalanches are endangered in the majority of cases. Safety
measures, such as the use of explosives or closures, are to be recommended in these places. The
conditions outside marked and open pistes are unfavourable. Avalanche runout zones in particular
warrant caution.
Around ten percent of all fatal accidents occur at this danger level.
9.6 Very high avalanche danger (level 5)
The snowpack is generally weakly bonded and therefore largely unstable (consistent with large
quantities of new snow accompanied by a fracture within same, or at transitions between new snow
and the old snowpack). Extensive weak layers can also exist deep inside the snowpack; these can
collapse if exposed to a heavy burden of overlying snow and give rise to large or very large
avalanches. Numerous large and, in many cases, very large natural avalanches are to be expected,
including in moderately steep terrain. Avalanches can also occur in the same place several times
and open up new paths. Extensive safety measures (closures and, in some circumstances,
evacuation etc.) are required. Fortunately, such disaster situations warranting danger level 5 very
rarely arise. In such instances, backcountry touring is not recommended and is usually impossible
in any case.
19
Fatal accidents have occurred at this danger level in particular during winters with large avalanches,
as in 1951, 1968, 1975, 1984 and 1999, and account for around 1% of the total.
10. Explanation of avalanche prone locations
10.1 General
The avalanche bulletin indicates not only the danger level, but also the terrain features that are
considered critical. A typical phrase is "Avalanche prone locations are to be found, in particular, on
west to north to southeast facing wind-loaded slopes above approximately 2000 m".
In order to interpret the information and plan backcountry tours sensibly, the slope angle, aspect,
altitude zone and type of slope are to be established by consulting the 1:25,000-scale maps
published by swisstopo.
10.2 Slope angle
Most skier avalanches occur at slope angles between 35 and 40 degrees. Especially if the danger
level is high or very high, isolated avalanches can also be released in areas with a slope angle of
less than 30 degrees.
The slope angle category stated in the avalanche bulletin indicates that slopes in that range are
especially critical. The following slope angle categories are used in the avalanche bulletin:
Moderately steep: Slope angle less
than 30°
Steep:
Steeper than 30°
Very steep:
Steeper than 35°
Extremely steep: Steeper than 40°
Long-term average: 3% of skier avalanches
This is the category that is cited most frequently in the
avalanche bulletin
This category is seldom cited in the avalanche bulletin
Slopes in this category are usually particularly unfavourable
as regards the type of terrain, proximity to the ridge or
ground condition as well. This category is cited in the
avalanche bulletin in combination with the low danger level
in particular.
The indicated values (e.g. steeper than 35°) must, of course, be assumed to be approximate. They
are to be regarded as guidelines, and slopes with broadly similar angles must be treated with
caution as well.
10.3 Slope aspect
A north facing slope falls to the north. If you are standing on a mountain summit looking towards
the north (with the sun on your back at midday), the north facing slope lies immediately in front of
and below you. In mid-winter, steeper north facing slopes are shaded by the mountains for long
periods and therefore not exposed to any direct solar radiation. In such aspects, settling and
bonding usually occur only slowly.
A south facing slope falls to the south and therefore receives sun regularly, even in mid-winter. As
a consequence, the snow generally settles faster and bonds more effectively on such slopes. In the
mornings, sunshine first strikes the east facing slopes. The last sunshine of the day strikes the west
facing slopes.
20
Shaded or shady slopes are more prevalent in mid-winter (when the sun is low in the sky) than in
springtime (when the sun rises higher and higher). Depending on the extent of shadow being cast
by the near horizon, slopes in any aspect can be shady, not only north facing slopes.
The terms "sun-exposed slopes" and the equivalent "sunny slopes" are to be interpreted likewise.
Wind-exposed or windward slopes face the wind. Snow lying on these slopes is usually blown
away.
Leeward, downwind or lee slopes face downwind (away from the wind). Snow blown off
windward slopes is deposited here. Lee slopes often have many times the average amount of snow
and are sometimes called "wind-loaded slopes" for this reason.
Windward and leeward slopes are significant aspects not only near mountain summits. They also
occur at large distances from summits, typically on the flanks of valleys with a prevailing wind
direction. In such situations, the wind can be diverted by the terrain and deviate significantly from
the naturally prevailing direction.
Steep slopes adjacent to the ridge line are generally situated close to pronounced crests that
connect peaks. They are often interspersed with rock and occur in all aspects.
10.4 Altitude zone
References to especially critical altitude zones are generally made in increments of 200 m. In the
case of dry avalanches, the altitude above which avalanches can occur is usually cited. For wet
avalanches, the cited altitude is the one below which they are most likely to occur. Formulations
referring to a range of altitudes, such as "between 2500 m and 3000 m", are seldom used.
The following terms are frequently used in the avalanche bulletin:
– low altitudes:
locations below approximately 1000 m
– intermediate altitudes: locations between approximately 1000 m and 2000 m
– high altitudes:
locations between approximately 2000 m and 3000 m
– high Alpine regions:
locations above approximately 3000 m
The tree line is also used as a reference. It denotes the transitional area between forest land, which
is sheltered from the wind, and open Alpine terrain, which is exposed to the wind. The tree line is
situated at the transition between intermediate to high altitude. It lies at approximately 2200 m in
central Valais and Engadine, 2000 m in the inneralpine regions and at the Southern flank of the
Alps, and 1800 m in the Prealps.
10.5 Other terminology describing especially critical terrain features
In connection with the accumulation of new snow drifts (during periods of snow transport), the
term "wind-loaded slope" is often used as well. A steep wind-loaded slope is one that is prone to
new snow drift accumulation, which is an especially critical phenomenon (see above). The terms
"gullies and bowls" and "areas adjacent to the ridge line" are also used in the avalanche
bulletin, usually in connection with snow drift accumulations. When gullies and bowls or areas
adjacent to the ridge line are indicated, the avalanche prone locations are generally restricted to
these types of terrain and are therefore relatively easy to localise. They also tend to cover small
areas.
10.6 Use of terms in the avalanche bulletin
As regards the prevalence of avalanche prone locations, the following sequence generally applies:
1) Steep slopes:
Avalanche prone locations are to be expected on all steep slopes of the indicated aspect and
altitude zone (including in gullies and bowls).
21
2) Wind-loaded slopes:
Avalanche prone locations are to be expected, in particular, on steep slopes of the indicated
aspect and altitude zone where snow drifts have been deposited on top of the snowpack
(including in gullies and bowls that are filled with snow drift accumulations).
3) Gullies and bowls / areas adjacent to the ridge line:
Avalanche prone locations are generally to be found, in particular, in gullies and bowls /
adjacent to the ridge line in the indicated aspect and altitude zone.
If the steepness of slope is not indicated when the terms "wind-loaded slopes" or "gullies and bowls
/ adjacent to the ridge line" are used, it can generally be assumed that the reference is to steep
wind-loaded slopes or steep gullies and bowls / areas adjacent to the ridge line. Otherwise, the
specific slope angle category precedes the relevant term, e.g. "very steep wind-loaded slopes".
10.7 Graphic depiction of especially critical areas in the danger map
The especially critical areas can be depicted graphically in the danger map (cf. Appendices 3 and 5).
The areas coloured black are particularly critical. The example alongside indicates the following:
the avalanche prone locations are to be found, in particular, on west to north to
northeast facing aspects above approximately 2600 m.
The aspects are depicted exactly as described by the text (west to north to
northeast facing). If the lower limit of the particularly critical altitude zone is
stated, the altitude is shown above the line, and the top part of the mountain
symbol is coloured black (as illustrated in the example alongside; this is the
typical situation in the case of dry avalanches). If the upper limit of the
particularly critical altitude zone is stated, the altitude is shown below the line,
and the bottom part of the mountain symbol is coloured black (this is the typical situation in the
case of wet avalanches).
Interpretation
The avalanche situation is most critical in the locations described as "avalanche prone". In other
areas, the avalanche danger is usually lower, but an avalanche bulletin cannot indicate the exact
extent to which the specific danger is reduced. No clearly defined boundaries exist between
adjacent areas with different danger levels, or at the margins of aspects and altitude zones which
are specifically cited. These marginal areas and intermediate zones of varying sizes cannot be
unequivocally assigned to either the favourable or unfavourable category and must therefore be
evaluated with care and prudence. At the margins of adjacent areas with different danger levels, it
is to be assumed that the transition zone or range extends for several kilometres (cf. Figure 4a). In
these places, due consideration is to be given to both danger assessments. The transition range is
about plus or minus one one-sixteenth segment of a circle for aspects (cf. Figure 4b) and plus or
minus 200 m for altitude zones (see Figure 4c). These numbers are not exact, but only indications
of magnitude. In the transition range or zone, both the more and the less favourable assessment can
apply.
22
Figure 4b:
Figure 4a:
Figure 4c:
Figures 4a to 4c: Note that the boundaries between danger levels, aspects and altitude zones are not exactly
defined.
It has become customary in backcountry touring to assume the danger level to be one level lower in
the areas that are not specifically indicated. This rule of thumb has proven largely reliable but, like
every rule, is subject to exceptions. It can be applied when planning backcountry tours, but does
not replace an assessment in the open terrain, especially since the danger level applies to an entire
region, not to an individual slope. Note that the avalanche warning service disregards this rule of
thumb when compiling the avalanche bulletin. When the particularly critical areas are designated,
therefore, no consideration is given to whether the danger level is exactly one level lower
elsewhere.
Most fatal avalanche accidents have occurred in core zones; that is to say, in areas where the slope
angle, slope aspect and altitude zone have matched those that were described as particularly critical.
This analysis disregards the danger level prevailing on those days when accidents occurred.
23
11. Additional information and recommendations for individual user
groups
11.1 General
In the discussions that led up to the introduction of a European avalanche danger scale, opinions
differed as to whether warnings about specific consequences and relevant recommendations for the
principal user groups should be included in the scale alongside the information concerning
snowpack stability and avalanche triggering probability. The French and Italian warning services
do not issue any warnings about consequences or any recommendations. The Austrian and German
warning services regard such warnings and recommendations as useful to some extent. In
Switzerland, additional warnings for certain user groups were already contained in the old
avalanche danger scale that was adopted in 1985. After conducting a nationwide survey among the
key user groups, the SLF decided to continue commenting on consequences and making
recommendations. It was motivated by the ongoing endeavour to make the avalanche bulletin more
readily understandable.
11.2 Permanent recommendations
The consequences and recommendations for transportation routes and settlements (Appendix
1, penultimate column) are targeted at those responsible for cantonal and communal avalanche
services, the relevant officials of the national and private railway systems, and the mountain
railway and cableway operators' heads of piste safety. Among the safety measures are the release of
avalanches with explosives (usually performed as a safeguarding measure), the closure of roads or
pistes, urging people to enter bunkers or shelters, or (in extremely critical situations) evacuating
people from individual buildings or entire localities. The safety measures to be taken in a specific
situation vary from case to case and are determined by those responsible for public safety.
The consequences and recommendations for persons outside secured zones (Appendix 1, final
column) are primarily targeted at snow sport participants. Persons depart from secured zones
typically when embarking on backcountry touring or other off-piste activities, including on
snowshoes or snowboards, and when they are in open terrain for professional reasons. The
individual danger level descriptions contain key words denoting consequences and
recommendations for such groups.
The information on conditions refers exclusively to the avalanche danger. The avalanche bulletin
only rarely remarks on the condition of the snow (powder snow, corn snow, breakable crust) and
weather conditions (fog, storm force winds), which are also potentially dangerous in some
circumstances.
Experience in the assessment of avalanche danger is best obtained by attending the various courses
offered by the Swiss Alpine Club, Jugend+Sport, the mountaineering schools, the ski and
snowboard associations or the armed forces.
The recommendations given in Appendix 1 are to be interpreted as good advice. After an
evaluation of the situation in open terrain, the decision as to how to respond to the avalanche
danger and the extent of acceptable risk lies with each individual.
11.3 Current recommendations
In certain situations, the avalanche bulletin contains additional recommendations of behaviour
adapted to the current conditions. The warning service issues such recommendations sparingly. As
a rule, they refer to users' training and experience (typically "Those with little experience in the
assessment of avalanche danger should remain on the pistes open to the general public", "Activities
on these slopes require a lot of experience", or "Those with little experience should avoid such
slopes").
24
Opinions as to whether the avalanche bulletin should contain current recommendations diverge
among the various European warning services. The Bavarian avalanche warning service, for
example, does not issue any recommendations as a matter of principle.
12. Geographical terminology
For the purposes of the avalanche bulletin, the Swiss Alps are divided into around 120 warning
regions (cf. Appendix 9). Groups consisting of several warning regions are formed, generally by
applying climatological or political criteria, and named according to convention as far as possible.
These names are also used by MeteoSwiss and all the other official natural hazard warning
authorities.
Appendix 10 shows the climatic and geographical division of the Swiss Alps into two zones: the
northern and southern flanks. Depending on the situation, reference can be made to the major
political regions shown in Appendix 11, which facilitates a more detailed subdivision. Expressions
such as "Lower Valais" and "Glarus Alps" are generally known. The names used for small districts,
however, call for good local geographical knowledge on the part of the user, which cannot be
assumed to exist among foreign visitors in particular.
The political subdivisions shown in Appendices 12 and 13 are seldom mentioned.
Appendix 14 shows the Main Alpine Ridge and the northern Alpine Ridge. The Main Alpine
Ridge extends approximately from the Great St Bernhard Pass via the Monte Rosa, Simplon,
Gotthard, Lukmanier, San Bernardino, Maloja and Bernina Passes to beyond Val Müstair. The
northern Alpine Ridge covers a belt from the Dent du Midi via the Wildstrubel and Jungfrau
regions, Gotthard, Tödi and Vorab, and into the Alpstein region.
The inneralpine regions are generally understood to encompass the regions between the Main
Alpine Ridge and the northern Alpine Ridge, namely central Valais, parts of northern and central
Grisons, and Engadine (Appendix 14).
An area of particular significance is the Gotthard region (Appendix 13). It consists of Obergoms,
the Grimsel region, Urseren, Tavetsch, the Upper Valle Leventina and Val Bedretto. The Grisons
southern valleys include Val Moesa and Val Calanca (collectively Moesano), Val Bregaglia, Val
Poschiavo and Val Müstair.
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, Bernese Oberland or eastern Bernese Oberland), but the backcountry touring area lies
mostly in the territory of Valais (Valais, Upper Valais, northern Valais or Goms). Furthermore, the
assignment of danger levels to regional border areas is indistinct. These intermediate areas cover
several kilometres (cf. Chapter 10). Those undertaking backcountry tours on skis or snowboards in
such areas must therefore consult the avalanche bulletin as a whole.
13. Supporting products
The supporting products complement the information contained in the avalanche bulletin and aid
its interpretation.
13.1 New snow maps
A new snow map showing the amount of new snow that has fallen in the previous 24 hours (new
snow 1 day) (cf. Appendix 15) and a similar map showing the amount of new snow that has fallen
in the previous 3 days (new snow 3 days) are published daily at 9.30 am. The interpolations and the
assignment of the data to the cross-hatched, standard new snow depth bands (0 to 1 cm, 1 to 10 cm,
10 to 25 cm, and 25 to 50 cm) take place automatically; no checks or corrections are made. Since
the majority of stations that capture the data are located at low and intermediate altitudes, the
25
situation depicted by the map can be difficult to interpret or inaccurate if the snowfall level is
above 1000 m. To aid interpretation, the raw data captured at station altitude are therefore indicated
as well.
13.2 Snow depth map
The snow depth map shows the calculated snow depth in a 1 x 1 km grid, based on measurements
taken by the SLF and MeteoSwiss measuring stations. On days with little cloud, the measurements
are supplemented by NOAA-AVHRR satellite data collected by the Remote Sensing Group at the
University of Bern. A snow coverage map is calculated from the satellite data in Bern.
Consideration is given to this map when the snow depth map is being plotted. The calculation of
the snow depth in the 1 x 1 km grid follows an approach that pays due regard to both the
dominating influence of the topography on snow depth, and the local measurements (cf. Appendix
16).
The snow depth map is generally published on Thursdays at around 10 am, but more frequently if
necessary. When consideration is given to the NOAA-AVHRR satellite data, the accuracy of the
snow depth calculation depends on clear skies. In some cases, the snow depth map is produced
without satellite data.
13.3 Snow depth at 2000 m or 2500 m
Every Thursday, and on other weekdays if marked changes occur, the snow depth map showing the
mean snow depth at 2000 metres (at 2500 m in the early and late winter months) is published at
about 10 am (cf. Appendix 17). It is based on measurements taken by the SLF and MeteoSwiss
measuring stations. The snow depth at 2000 m is calculated from all the data captured between
1600 m and 2400 m, and the depth at 2500 m is calculated from all the data captured between 2100
m and 2900 m. This map covers the entire territory of the Swiss Alps and provides a general survey
of the current snow depth on horizontal surfaces. Regions with identical or similar snow depths are
indicated by colour coding or cross-hatching.
When interpreting the map for parts of the terrain at lower or higher altitudes, note that the snow
depth gradient can vary greatly. It generally lies in the range from 5 to 20 cm per 100 metres
altitude. Also note that the values refer to horizontal surfaces; the snow depth on slopes can often
be very different. At the start and end of the season when there is less snow on the ground, the
mean snow depth at 2500 metres is indicated, as stated in the map's title.
13.4 Snow depth compared with long-term mean
A map that compares the current snow depth with the long-term mean (cf. Appendix 18) is
published alongside the snow depth map (cf. Chapters 13.2 and 13.3). It is based on the data
collected by observer (comparative) stations with records of measurement series covering a period
of more than 10 consecutive years. The data captured by stations above 1200 m are generally used.
The following categories are applied:
< 60%:
well below average
60 to 90%:
below average
90 to 110%:
average
110 to 140%:
above average
> 140%:
well above average
If there is a prevalence of values < 60% and significantly less than 30%, and a prevalence of values
> 140% and significantly greater than 170%, these are reported with greater precision.
13.5 Snowpack stability map
The map shows the findings of snowpack analyses, as interpreted by the avalanche warning service.
These analyses provide a snapshot of the snowpack at a specific time and place, and are assigned to
26
one of three stability categories. Clicking on individual symbols pulls up the snow profiles (cf.
Appendix 19).
The snowpack stability on an individual slope cannot be described because it can vary from one
place to another, and the volume of available data is insufficient. On the other hand, by referencing
several snow profiles, the regional snowpack stability existing at the time the profiles were taken
can be evaluated generally.
The following limitations apply:
• The information refers to the time the profile was taken. If the condition of the snowpack
does not change, the information can remain valid for a prolonged period. If, on the other
hand, new snow has fallen and not yet bonded well with the old snowpack, the snowpack
stability changes and the validity of the information is restricted. In any such case, the
snowpack will have become thicker and has usually changed in the period since the profile
was taken.
• The volume of information varies. Some regions generate more information and more
current information than others.
• The snowpack stability map is updated as soon as new snow profiles are available.
More detailed information concerning the snowpack stability map is available on the internet at
www.slf.ch.
13.6 Weekly report
Throughout the whole year, the weekly report describes and comments on the weather conditions
that are relevant to the avalanche danger, changes in the layering and stability of the snowpack, as
well as other aspects of the snow and avalanche situation in the Swiss Alps. The reports are
supported by thematic maps, photographs and measured values. Additional remarks explaining
specific processes and occurrences in a period are included whenever necessary.
Reviews of the recent period are published weekly in the peak winter season winter and monthly in
the off-peak winter season and during the summer. The reporting year coincides with the
hydrological year, running from October 1st to September 30th. The monthly reports are made
available at the beginning of the following month, and the weekly reports are available on
Thursday evenings in German, and Friday evenings in French. Use the menu in the left margin to
select specific periods.
In the early summer (June), the winter is summarised in an annual report. Once the avalanche
accident reports have been compiled, the annual and accident reports are published together in a
German document entitled "Schnee- und Lawinen in den Schweizer Alpen" (Snow and Avalanches
in the Swiss Alps). It is also known as the "Winterbericht" (Winter Report) and is made available
for downloading as a pdf file.
13.7. Icons
The icons (see Appendices 2) provide simple and clear information about the avalanche danger to
the general public. This brief information is intended to encourage snow sport participants and
others to obtain more detailed information as well from www.slf.ch. The icons can be used either
as a map or as single illustrations (see Appendices 2 and 6), typically to add a pictorial
representation of the avalanche danger level for the region concerned to local weather information.
27
14. Distribution channels and how to consult the products
Overview
Internet:
www.slf.ch
Smartphones:
White Risk
app
SMS
RSS
Avalanche
bulletin

Snow maps
Station data





"SLFSOMMER"
SMS


Internet
Address: www.slf.ch
Products: Avalanche bulletin, snow maps, data captured by automatic measuring stations,
additional and detailed information concerning snow and avalanches, Online form „submit
observation“.
Smartphones
SLF App “White Risk”
Free app for iPhone and Android smartphones (available from the iTunes or
Google Play store)
Products: Avalanche bulletin, snow maps, data captured by automatic
measuring stations, background knowledge on the subject of avalanche
science, tools for use in the field and a form „submit observation“.
"SLFSOMMER" SMS
If you wish to be notified of an unscheduled avalanche bulletin via SMS, please send an SMS with
the message START SLF SOMMER to tel. no. 9234. Shortly after such a bulletin is issued, you
will then automatically receive an SMS informing you of its publication. You can cancel the
service anytime by texting STOP SLF SOMMER.
Cost: CHF 0.20 per SMS
RSS
Address: www.slf.ch/dienstleistungen/rss/index_EN
Product: Avalanche bulletin
Radio
Radio SRF 1: Daily at around 4.50 pm
Radio SRF 3: At irregular intervals, in particular when an elevated avalanche danger exists
Radio Südostschweiz: Daily at around 5.50 pm
RadioRumantsch: Fridays 5.50 pm
Rhône FM: Fridays around 6.15 pm (in collaboration with the branch station in Sion).
RSI Rete 1: Fridays around 4 pm (in collaboration with MeteoSwiss)
Radio Fiume Ticino: Fridays around 5.15 pm (in collaboration with MeteoSwiss)
Radio 3I: Saturdays around 7.40 am (in collaboration with MeteoSwiss)
Other local radio stations: At irregular intervals, in particular when an elevated avalanche danger
exists
28
Television
SF 1, SF info, TSR, TSI: During the weather forecast, shortly before or after 8 pm; often on
Fridays, but occasionally on other days as well
Natural-hazards portal and MeteoSwiss app
The natural-hazards portal (www.naturgefahren.ch) and the MeteoSwiss app provide a synopsis of
the current natural hazard situation in Switzerland. It shows the danger levels in all the natural
hazard processes for which warnings are issued (rain, thunderstorms, flood, snow, avalanches, heat
waves, frost, slippery roads, wind, forest fires, earthquakes) and contains general information on
the individual natural hazards and how to respond to them. This information is supplied by the
federal government's natural hazard agencies, namely the Federal Office of Meteorology and
Climatology (MeteoSwiss), National Environmental Agency (BAFU), WSL Institute for Snow and
Avalanche Research SLF, and the Swiss Seismological Service (SED). The MeteoSwiss and
WhiteRisk apps are cross-linked in order to give users the most convenient access possible to
detailed information.
15. Feedback on avalanche danger
Verification of the avalanche danger entails the subsequent, independent investigation of the
avalanche situation based on additional field tests, avalanche observation, avalanche accident
analyses, or interviewing skiers by way of questionnaires. The goal is to review the announced
danger levels and the parts of terrain that were considered to be especially critical. Relevant
feedback from users contributes much to improving the avalanche bulletin. The avalanche warning
service is eager to receive all feedback, in particular if an actual occurrence differs from the
assessment of the danger published in the avalanche bulletin.
Feedback can be provided in several different ways:
- Online form at www.slf.ch/lawinenbulletin/rueckmeldung/index_EN
- SLF WhiteRisk App
If such notification arrives in time (submitted by 2:30 pm), it can even be integrated in the next
day's avalanche bulletin.
16. Closing remarks
Avalanches do not occur by chance, and people are usually affected by them more through their
own behaviour than through providence. Most avalanche accidents are attributable to slab
avalanches which, in about 90% of cases, are triggered by the victims or members of their group.
Note that every avalanche, even a minor snow slide, can be dangerous. Caution is warranted not
only in view of the danger of being buried, but also because avalanches can sweep people along
and cause them to fall.
The following points are therefore essential if the risk is to be minimised:
1. Education:
If risk is to be eliminated as far as possible, education and training in the assessment of
avalanche danger is essential for all activities in wintry terrain outside marked and open pistes
and snow sport regions. One of the purposes served by such education is to develop not only an
understanding of the spatial and temporal changes that take place continuously inside the
snowpack and across the terrain, but also the skills required to engage in outdoor pursuits to the
greatest possible extent. Each of these aspects calls for practice. Avalanche courses are offered
by various organisations for different levels of expertise.
2. Information:
29
Information about the avalanche danger is to be obtained prior to engaging in activities in wintry
terrain outside marked and open pistes and snow sport regions. Besides the avalanche bulletin
and the various supporting products of the SLF, which serve as a basis, local information from
mountain railway and cableway operators, mountaineering schools, refuge wardens etc., together
with your own observations, can provide important information on the avalanche danger.
3. Emergency equipment:
The following items are among the emergency equipment to be carried by those engaging in
activities in wintry terrain outside marked and open pistes and snow sport regions:
Transceiver
Shovel
Probe
In the stressful circumstances of an accident, however, the ability to use this equipment correctly
depends on regular practice. Additional items of emergency equipment, such as an avalanche
airbag, are recommended.
4. Conduct:
Finally, risk is reduced by defensive behaviour, adapted as well as possible to the specific
situation.
30
Appendix:
Appendix 1:
Appendix 2:
Appendix 3:
Appendix 4:
Appendix 5.1:
Appendix 5.2:
Appendix 5.3:
Appendix 6:
Appendix 7:
Appendix 8:
Appendix 9:
Appendix 10:
Appendix 11:
Appendix 12:
A ppendix 13:
Appendix 14:
Appendix 15:
Appendix 16:
Appendix 17:
Appendix 18:
Appendix 19:
Appendix 20:
European danger scale with recommendations ...........................................32
Overview of European avalanche danger scales .........................................33
Specimen avalanche bulletin on the internet –
danger map including danger description....................................................34
Specimen avalanche bulletin on the internet – snowpack and weather.......35
Specimen full avalanche bulletin (for printing)...........................................36
Specimen full avalanche bulletin (for printing)...........................................37
Specimen regional danger map (for printing)..............................................38
Specimen icon map......................................................................................39
SLF network of observer stations ................................................................40
IMIS (and SwissMetNet) stations (snow stations) ......................................40
Geographical terminology V - the smallest units the 123 warning regions ..............................................................................41
Geographical terminology I - northern and southern flank of the Alps ......42
Geographical terminology II - major political regions ................................42
Geographical terminology III - political subregions 1 ................................43
Geographical terminology IV - political subregions 2 ................................43
Geographical terminology VI: Main Alpine Ridge, northern
Alpine Ridge and inneralpine regions .........................................................44
Specimen new snow map (1 day) ................................................................44
Specimen snow depth map ..........................................................................45
Specimen snow depth map for 2000 m .......................................................45
Specimen snow depth map showing comparison with long-term mean
values ...........................................................................................................46
Specimen snowpack stability map ...............................................................46
Typical danger situations (avalanche problems) .........................................47
31
Appendix 1: European danger scale with recommendations
Danger level
Snowpack stability
Avalanche triggering probability
Consequences for transportation routes
and settlements / recommendations
Consequences for persons outside secured zones /
recommendations
5
very high
The snowpack is poorly
bonded and largely unstable in
general.
Many large and multiple very large natural
avalanches are expected, even in moderately steep
terrain.
Acute danger.
Comprehensive safety measures.
Highly unfavourable conditions.
Avoid open terrain.
4
high
The snowpack is poorly bonded
on most steep slopes*.
Triggering is likely even from low additional loads** on
many steep slopes. In some cases, numerous mediumsized and often large-sized natural avalanches can be
expected.
Many exposed sectors are endangered.
Safety measures recommended in those
places.
Unfavourable conditions.
Extensive experience in the assessment of avalanche
danger is required. Remain in moderately steep
terrain / heed avalanche run out zones.
3
considerable
The snowpack is moderately to
poorly bonded on many steep
slopes*.
Triggering is possible, even from low additional loads**
particularly on those steep slopes indicated in the
bulletin. In some cases medium-sized, in isolated cases
large-sized natural avalanches are possible.
Isolated exposed sectors are endangered.
Some safety measures recommended in
those places.
Partially unfavourable conditions.
Experience in the assessment of avalanche danger is
required. Steep slopes of indicated aspects and
altitude zones should be avoided if possible.
2
moderate
The snowpack is only
moderately well bonded
on some steep slopes*,
otherwise well bonded in general.
Triggering is possible primarily from high additional
loads**, particularly on those steep slopes indicated in
the bulletin. Large-sized natural avalanches are unlikely.
Low danger of natural avalanches.
Mostly favourable conditions.
Careful route selection, especially on steep slopes of
indicated aspects and altitude zones.
1
low
The snowpack is well
bonded and stable in general.
Triggering is generally possible only from
high additional loads** in isolated areas of
very steep, extreme terrain. Only sluffs
and small-sized natural avalanches are possible.
No danger
Generally safe conditions
Explanations:
* generally explained in greater detail in Avalanche Bulletin (e.g. altitude zone, aspect, type of terrain)
** Additional load:
- natural: without human assistance
- high (e.g. group of skiers without spacing, snowmobile/groomer, avalanche blasting)
- aspect: the compass direction in which a downward slope faces
- low (e.g. single skier, snowboarder, snowshoe hiker)
- exposed: especially exposed to danger
 moderately steep terrain: slopes flatter than about 30 degrees
 steep slopes: slopes with an angle greater than about 30 degrees
 steep extreme terrain:: those which are particularly unfavourable as regards slope angle (usually steeper than about 40°), terrain profile, proximity to ridge, roughness of underlying ground
“conditions” refers exclusively to the avalanche danger. The avalanche bulletin only rarely remarks on the condition of the snow (powder snow, corn snow, breakable crust) and weather conditions (fog,
storm force winds), which are also potentially dangerous in some circumstances.
32
Appendix 2:
5
4
3
2
1
Overview of European avalanche danger scales
English
Danger level
very high
high
considerable
moderate
low
Deutsch
Gefahrenstufe
sehr gross
gross
erheblich
mässig
gering
français
Degré de danger
très fort
fort
marqué
limité
faible
italiano
Scala del pericolo
molto forte
forte
marcato
moderato
debole
The colours of the various avalanche danger levels have also been standardised in Europe:
very high
red/black
high
considerable
moderate
low
red
orange
yellow
green
255,000,000 (RGB)
000,000,000 (RGB)
255,000,000 (RGB)
255,153,000 (RGB)
255,255,000 (RGB)
204,255,102 (RGB)
Icons:
Danger level
5
Very high
4
high
3
considerable
2
Moderate
1
Low
Danger of wet snow avalanches increasing avalanche danger during the day
no danger level
33
Appendix 3:
Specimen avalanche bulletin on the internet – danger map including danger
description
34
Appendix 4:
Specimen avalanche bulletin on the internet – snowpack and weather
35
Appendix 5.1:
Specimen full avalanche bulletin (for printing)
36
Appendix 5.2:
Specimen full avalanche bulletin (for printing)
37
Appendix 5.3:
Specimen regional danger map (for printing)
38
Appendix 6:
Specimen icon map
39
Appendix 7:
SLF network of observer stations
Appendix 8:
IMIS (and SwissMetNet) stations (snow stations)
40
Appendix 9:
Geographical terminology V - the smallest units - the 123 warning regions
1111
1112
1113
1114
1121
1211
1212
1213
1221
1222
1223
1224
1225
1226
1227
1228
1231
1232
1233
1234
1241
1242
1243
1244
1245
1246
1247
1311
1312
Western Part of the
Northern flank of the Alps
Vaud Prealps
Pays d'Enhaut
Aigle-Leysin
Bex-Villars
Fribourg Alps
Western Bernese Prealps
Eastern Bernese Prealps
Hohgant
Niedersimmental
Gstaad
Wildhorn
Lenk
Iffigen
Adelboden
Engstligen
Obersimmental
Kandersteg
Blüemlisalp
Lauterbrunnen
Jungfrau – Schilthorn
Brienz-Interlaken
Grindelwald
Schreckhorn
Hasliberg – Rosenlaui
Guttannen
Gadmertal
Grimsel Pass
Vouvry
Monthey-Val d'Illiez
2111
2121
2122
Central Part of the
Entlebuch
Glaubenberg
Engelberg
2123
2131
2132
2211
2212
2221
2222
2223
2224
Melchtal
Schwyz Prealps
Muotatal
Schächental
Uri Rotstock
Meiental
Maderanertal
Northern Urseren
Southern Urseren
4222
4223
4231
4232
4241
4242
4243
4244
Upper Mattertal
Upper Saastal
Northern Simplon region
Southern Simplon region
Reckingen
Binntal
Northern Obergoms
Southern Obergoms
6121
6122
6131
6132
6211
6212
Lower Valle Maggia
Riviera
Lugano area
Mendrisio area
alto Moesano
basso Moesano
3111
3112
3113
3211
3221
3222
3223
3311
Eastern Part of the
Northern and central Glarus
Southern Glarus-Grosstal
Southern Glarus-Sernftal
Appenzell Alps
Toggenburg
Alpstein – Alvier
St Gallen Oberland
Liechtenstein
4111
4112
4113
4114
4115
4116
4121
4122
4123
4124
4125
4211
4212
4213
4221
Valais
Emosson
Génépi
Val d'Entremont-Val Ferret
Conthey-Fully
Martigny-Verbier
Haut Val de Bagnes
Montana
Val d'Hérens
Arolla
Val d'Anniviers
Mountet
Lötschental
Turtmanntal
Aletsch region
Lower Valleys of Visp
5111
5112
5113
5121
5122
5123
5124
5211
5212
5214
5215
5216
5221
5222
5223
5231
5232
5233
5234
Northern and Central Grisons
Northern Prättigau
Southern Prättigau
Western Silvretta
Calanda
Schanfigg
Davos
Flims
Northern Tujetsch
Southern Tujetsch
Obersaxen – Safien Valley
Val Sumvitg
Zervreila
Domleschg – Lenzerheide
Schams
Rheinwald
Albulatal
Savognin
Avers
Bivio
7111
7112
7113
7114
7115
7121
7122
7123
7124
7125
7126
7211
7221
7222
7231
Engadine / eastern Part of the
Southern flank of the Alps
Corvatsch
Bernina region
Zuoz
St Moritz
Val Chamuera
Samnaun
Eastern Silvretta
Sur Tasna
Val Suot
Val dal Spöl
Val S-charl
Val Bregaglia
Upper Val Poschiavo
Lower Val Poschiavo
Val Müstair
Jura / Swiss plateau
western Jura
main ridge of the Jura chain
north of the Jura chain
western Swiss Plateau
central Swiss Plateau
eastern Swiss Plateau
6111
6112
6113
6114
6115
Central Part of the
Southern flank of the Alps
Val Bedretto
Upper Valle Leventina
Val Blenio
Upper Valle Maggia
Lower Valle Leventina
8111
8121
8122
9111
9211
9311
41
Appendix 10:
Geographical terminology I - northern and southern flank of the Alps
Appendix 11:
Geographical terminology II - major political regions
42
Appendix 12:
Geographical terminology III - political subregions 1
A ppendix 13:
Geographical terminology IV - political subregions 2
43
Appendix 14:
Geographical terminology VI: Main Alpine Ridge, northern Alpine Ridge
and inneralpine regions
Appendix 15:
Specimen new snow map (1 day)
44
Appendix 16:
Specimen snow depth map
Appendix 17:
Specimen snow depth map for 2000 m
45
Appendix 18:
Specimen snow depth map showing comparison with long-term mean values
Appendix 19:
Specimen snowpack stability map
46
Appendix 20: Typical danger situations (avalanche problems)
Fig. 1: Danger map showing highlighted region and the relevant danger description. The description contains the
following elements:
A - Danger level ("How great is the avalanche danger?")
B - Avalanche problem ("What is the main problem?")
C - Avalanche prone locations (core zone) ("Where in particular does the avalanche problem prevail?")
D - Description ("What are the characteristics of the avalanche problem?")
The danger description that forms part of the avalanche bulletin always cites one or more typical
avalanche situations or avalanche problems. The purpose is to focus attention on the current
avalanche problem. This practice makes use of the human brain's capacity to recognise and
interpret recurring characteristics. Each problem has a different cause and calls for a specific
response appropriate to the situation.
Several avalanche problems can occur at once, but the avalanche bulletin does not describe more
than three problems at a time.
The avalanche problems cited in the avalanche bulletin are described briefly below.
• New snow
• Snow drifts
• Old snow
• Wet avalanches (in the course of the day)
• Gliding avalanches
• Favourable situation
47
New snow
New fallen snow imposes an additional load on the snowpack underneath and forms a new layer. While it is
falling and generally for up to around three days thereafter, the freshly fallen snow seldom bonds sufficiently
well with the old snowpack.
The following factors are especially important in case of new snow:
• The quantity of new snow that has fallen. If the "critical quantity of new snow" has been reached, a
"considerable" avalanche danger (level 3) or higher must be assumed to exist. A critical quantity is:
• 10 to 20 cm in unfavourable conditions (strong wind, cold, unfavourable existing surface)
• 20 to 30 cm in moderate conditions
• 30 to 50 cm in favourable conditions (little wind, warm, favourable existing surface)
• The composition or quality of the old snowpack prior to the snowfall
• Unfavourable: surface hoar, a soft snowpack that is smooth over an extensive area, or a weakly
bonded old snowpack (in this case, the old snow problem must be cited as well)
• Favourable: small-area substantial inconsistencies in the old snowpack
Avalanche prone
• Over a wide area
locations
• Often becoming more precarious at higher altitudes
Indicated by
• (Critical) quantity of new snow
• Frequent alarm signs: in particular recent slab avalanches
Danger level
Often considerable (level 3), especially if the "critical quantity of new snow" is
reached
Recommended action
For planning purposes, apply the reduction method – depending on the
circumstances, do not launch a tour for the time being
Snow drift
When snow is transported by the wind, new snow drift accumulations form. The wind can transport freshly
fallen snow and/or loosely bonded old snow. Snow drift can therefore accumulate even in the most glorious
weather. Snow drifts are always well bonded. A warning of a snow drift situation is issued when new snow drift
accumulations have formed over the last three days or so.
The following factors are especially important in case of a snow drift situation:
• The age of the snow drift
• New snow drift accumulations are generally prone to triggering but not always easy to recognise.
The weather of recent days is a key indicator.
• The composition or quality of the old snowpack underneath the snow drift
• Unfavourable: surface hoar, a soft snowpack that is smooth over an extensive area, or a weakly
bonded old snowpack (in this case, the old snow problem must be cited as well)
• Favourable: small-scale substantial inconsistencies in the old snowpack
• Experience and good visibility: in many cases, these factors can allow snow drift accumulations to be
bypassed
Avalanche prone
• Subject to considerable local variations
locations
• Locations sheltered from the wind (bowls, abrupt changes in slope angle etc.)
• More prevalent at higher altitude and adjacent to the ridge line
Indicated by
• Snow formations caused by the wind, such as sastrugi or dunes
• Frequent alarm signs: whumpfing sounds, cracks, remote triggering and recent
slab avalanches
Danger level
Mostly moderate (level 2) or considerable (level 3)
Recommended action
Avoid new snow drift accumulations
48
Old snow
When the snowpack has for several days not been modified by precipitation, wind or melt processes, the
avalanche danger is determined by its deeper layers. If the snowpack contains long-enduring weak layers, an
old snow situation is said to exist. Such situations are long-lasting; they can persist for several weeks, months or
even an entire winter.
Old snow situations are difficult to assess. The following factors are therefore especially important:
• Defensive behaviour / damage limitation
Maintain spacing between individuals, descend very steep slopes one person at a time
• The information contained in the avalanche bulletin
The general condition of the snowpack is described in the daily avalanche bulletin under the heading
Snowpack and weather. The danger description (Fig. 1) also indicates whether the weak layers are near the
ground or nearer the surface of the snowpack. Conclusions can therefore be drawn concerning the likely
slab thickness. In addition to the daily text, the avalanche warning service also publishes a stability map
with snowpack analyses covering the Swiss Alps.
Avalanche prone
• Mostly not very prevalent, but avalanches can reach medium size
locations
• Often in areas where the snow cover is rather shallow, typically at the
transition from a broad ridge into a bowl or in rocky terrain
• Frequently on north-facing slopes
• Frequently in inneralpine regions
Indicated by
• Snow profiles and stability tests showing long-enduring weak layers
• Rare alarm signs: isolated whumpfing sounds
Danger level
Often moderate (level 2), mostly in the absence of avalanches within a region for
several days
Recommended action
Caution and restraint are imperative. The reduction method can be applied, but not
relied upon exclusively.
Wet avalanches (as the day progresses)
The penetration of water can quickly weaken the snowpack. The danger situation generally passes, however,
within a few hours. Two processes in particular give rise to water ingress:
• Warming during the day and significant solar radiation in the spring prompt the melting of surface snow
and the penetration of water into the snowpack.
• Rain introduces large quantities of snow into the snowpack within a short time. The rain moistens and
warms the snowpack and is an additional weight load.
Since the timing and location of the danger arising in a wet snow situation can vary greatly, the avalanche
bulletin defines the prevailing situation more precisely:
• Wet avalanches: if the situation is already unfavourable in the morning (rain, after a very warm and
overcast night)
• Wet avalanches during the day: if conditions are favourable in the morning and the danger is expected to
increase as the day progresses (classic springtime situation)
The following factors are especially important if there is a danger of wet avalanches:
• Were the skies clear during the night so that the snow surface was able to freeze and form a sturdy crust?
In such circumstances the situation in the morning is usually favourable. After an overcast night or in the
event of rain, the danger often already exists in the morning.
• Time schedule
Start out early and return early in the day
Avalanche prone
• Mostly depending on the aspect (except in the event of rain)
locations
• Conditions are sometimes better at higher than at lower altitudes
• Often in the vicinity of warming rock at first
• Pay close heed to the runout zones of large natural avalanches
49
Indicated by
Danger level
Recommended action
• A soaked, moist top layer or snowpack
• Sinking deep into the snow when wearing/not wearing skis
• Frequent alarm signs: natural slab and loose snow avalanches in particular
In springtime conditions often a favourable situation in the morning but increasing
thereafter to moderate or considerable danger (level 2 or 3)
Adhere to a rigid time schedule; find out whether skies were clear during the night
Gliding avalanches
When a gliding avalanche occurs, the entire snowpack slides on the smooth substratum, typically consisting of
grass or slabs of rock. The sliding movement is dependent on a moist bottom layer of snow at the interface with
the ground.
In mid-winter the moisture is introduced from underneath, from the warm and possibly moist ground. In such
conditions, gliding avalanches can occur at any time of day or night and even when the air temperature is low.
Apart from the near-ground "lubricating layer", the snowpack is dry.
In the spring the moisture is introduced mostly from above in the form of melt water. When these conditions
prevail, the incidence of gliding avalanches in the latter part of the day increases.
The following factors are especially important if there is a danger of gliding avalanches:
• As far as possible, avoid areas where gaps ("glide cracks") have opened in the snowpack
Avalanche prone
• Often in the vicinity of glide cracks
locations
• The avalanches are released not only by people, but also naturally
 Avoid runout zones
Indicated by
• Gaps in the snowpack ("glide cracks")
Danger level
Low or moderate (level 1 or 2). The avalanche bulletin only seldom issues a
warning describing gliding avalanches as the main danger, but frequently cites
them as an additional danger.
Recommended action
Avoid areas in the vicinity of glide cracks
Favourable situation
If none of the forenamed avalanche problems is crucial for an assessment of the avalanche danger, the
avalanche situation is considered favourable. Such conditions are characterised by a snowpack with only a few
layers having similar properties.
In these circumstances, avalanches can occur only in isolated cases and in particular in extremely steep terrain.
Besides the danger of being buried, the danger of falling in particular warrants caution.
Danger level
Low (level 1)
50

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