Reading the avalanche forecast

The avalanche forecast is the single source that has changed Norwegian ski touring most over the past twenty years. Before 2013, avalanche assessment was a skill you mainly had to build yourself, through courses, experience and local knowledge. After varsom.no was launched on 14 January 2013, there has been a daily professional basis that covers the whole of Norway, kept up to date by avalanche forecasters who are actually out in the terrain. It is an infrastructure built with public funds — run by NVE in cooperation with the Norwegian Meteorological Institute, Statens vegvesen and Bane NOR — and it is free to everyone.

But the forecast is not a guarantee. It is a regional assessment for an area of at least 100 km², based on models, data from automatic stations, and observations. It tells you the probability of avalanches in that area in general. It does not tell you what is happening on the one wind-loaded slope you are planning to traverse. The difference between reading the forecast and understanding it is the difference between calculating yourself safe and being safe.

The danger-level scale 1–5

The avalanche forecast uses a common European scale (EAWS) with five levels:

1 — Low (green): Avalanches are most likely on steep terrain over 30 degrees, but they are small and require you to trigger them yourself. Generally safe, but stay alert in extremely steep terrain.
2 — Moderate (yellow): Avalanches can be triggered in isolated cases. Check exposed terrain, consider your route choice.
3 — Considerable (orange): Avalanches can be triggered easily in many situations. The most common danger level in the main season, and at the same time the one where precise terrain assessment is critical.
4 — High (red): Naturally triggered avalanches may occur. Fewer are needed to trigger an avalanche. Travel in avalanche terrain is advised against.
5 — Very high (dark red): Many large natural avalanches. Travel in terrain above the tree line is advised against whatever the route.

The most common misunderstanding is to think that danger level 1 is safe everywhere and danger level 3 is safe outside avalanche terrain. Danger level 1 is not a free pass — it means the risk is low, not zero. Danger level 3 is not automatically dangerous — but it means the one wind-loaded slope you cross may give way even if the plateau is otherwise safe.

For a typical topptur in the core season, danger levels 2 and 3 are the norm. Levels 4 and 5 are rare, but they occur several times a season and are an explicit reason to cancel or switch to less exposed routes.

The avalanche problem — the most important thing under the danger level

Each day the forecast is published, it also gives one or more avalanche problems that tell you what kind of avalanche is most likely. This is often more important information than the danger level itself, because it governs what kind of terrain you need to be careful in.

The main types Varsom uses:

New-snow slab avalanches arise when fresh new snow bonds to underlying layers that do not hold. Most common during and immediately after snowfall. They can be triggered on steep terrain, on wind-loaded slopes where the new snow has settled.

Wind-slab avalanches form when strong wind transports snow and deposits it on lee faces and in drifts. The result is a hard slab on the surface that can release if it is weak underneath. A classic problem after windy days — you often feel the wind slab as a hollow, hard layer as you cross it.

A persistent weak layer is a layer deep in the snowpack that formed early in the season and is still unstable. A classic case is when a cold spell in January builds up a thin surface layer of depth hoar (cup crystals) that later snowfall then buries. It can be triggered weeks or months after it formed, and it is the avalanche type that takes the most lives, because it is hard to see.

Wet loose-snow avalanches and wet slab avalanches form when mild weather or rain destabilises the snowpack. Classic in the spring transition periods and on sunny spring days when the snow melts quickly.

Glide avalanches are the whole snowpack sliding on the ground when friction becomes too low — typically on grass or bare rock under dense snow. They are almost impossible to predict precisely, but they often give themselves away with characteristic ‘glide cracks’ (longitudinal cracks) on the surface days before they release.

For anyone reading the forecast, the main point is this: the avalanche problem tells you which terrain features are critical. A persistent weak layer means you must be careful everywhere, not just on the steepest wind-loaded slopes. Wind slab means you must watch lee ridges and drifts. Glide avalanches mean you must avoid the specific mountainsides where they have appeared.

Exposed terrain — where the avalanche can reach you

The forecast also gives an assessment of ‘exposed terrain’ — that is, how large a proportion of the terrain relevant to your route is actually avalanche-prone. This comes down to three main factors:

Steepness over 30 degrees is necessary for an avalanche. Most avalanches release in 35–45-degree terrain.
Wind-loaded slopes and overhanging snow increase the risk — even if you are not standing on steep terrain yourself, you may be in the run-out zone of a higher slope.
The tree line and terrain transitions are often areas where unstable snowpack concentrates.

In practice this means that a ski tour across a flat plateau can be low-risk even at danger level 3, while a topptur in steep mountain terrain is high-risk even at danger level 2 if the wind-loaded slope holds a persistent weak layer.

Map apps such as UT.no, Toporute or Strava have slope-angle shading that shows you what is over 30 degrees. Learning to read it is a fundamental skill — translating flat maps into actual steepness in the terrain.

Local signs while out

Besides the forecast, there are signals in the terrain that tell you immediately whether the snowpack is unstable. Experienced skiers register them almost automatically:

Recent avalanches in the area — the clearest indicator. If you see fresh crown faces or avalanche debris, the snowpack is actively unstable.
Whumpfing sounds beneath you as you walk — that is the top layer ‘settling’ because it is weak. The classic sound is a deep, muffled ‘whumpf’.
Cracks opening up around your skis — especially wind-slab cracks as you cross a lee ridge.
Rolling snow (snow that rolls in front of the ski like large cakes) — a sign of damp, unstable surface snow.
A sudden change in snow type as you walk — from hard to soft or the other way round often indicates a buried layer.

None of these is a sure sign on its own, but several together are. Recent avalanches + whumpfing sounds + steep terrain are a categorical reason to turn back, whatever the forecast says.

Three sources, not one

Serious ski-tour planners commonly use three sources at the same time:

Varsom for the regional danger level and avalanche problem
Yr.no or storm.no for the weather forecast — wind, temperature, precipitation over the past 24 hours
Local observations — Instagram groups for the area, the local mountain-sports club, or contact with people who have been out in recent days

For popular areas (Hurrungane, Sunnmøre, Lyngen) there are Facebook groups and local reporting channels where people share observations. This is often the freshest information you will get.

When to cancel

It is not necessarily the forecast’s danger level that decides whether you go. It is the combination of danger level, avalanche problem, terrain and your own experience. Even so, some combinations are categorical reasons to cancel or choose a different route:

Danger level 4 or 5 — do not go into avalanche terrain, and consider whether the day is viable at all
A persistent weak layer + steep terrain — even at danger level 2 this is a classic death trap
Danger level 3 + strong wind in the past 24 hours — the wind-slab problem is fresh and unpredictable
Mild weather + steep terrain — the wet-avalanche danger rises quickly and unpredictably
No observations from recent days in an area — you have too little information

Cancelling is not a defeat. It is the most common decision among experienced ski tourers. In a typical winter, most of them cancel more planned trips than they complete.

The Vassdalen accident and why the system exists

Norway’s modern avalanche infrastructure has been built gradually since the 1970s, but one event is a clear point of reference: the Vassdalen accident on 5 March 1986. A signals and engineer company from Brigade Nord was caught by a large slab avalanche during the NATO exercise Anchor Express. 16 soldiers died — the Armed Forces’ worst peacetime accident. NGI experts had tried to warn beforehand; the message ‘got lost in the system’.

After Vassdalen, military avalanche dogs, annual avalanche courses in the Armed Forces, avalanche maps and upgraded equipment were introduced. NGI, which had been given responsibility for avalanche research by the Storting in 1972, had its mandate strengthened. Civilian avalanche forecasting followed gradually, with varsom.no tying it all together from 2013.

It is worth remembering that this infrastructure is human-made and fairly new. Thirty years ago you had to phone NGI or rely on local knowledge. Today you have the forecast in your pocket — and that is a change in the premises for what a safe ski tour is.

Next steps

If you are new to avalanche assessment: take an introductory avalanche course. NVE-approved courses run by local mountain-sports clubs, NSF, or companies offering avalanche courses are the right place to start. They typically take a weekend or two evening sessions, and they give you vocabulary and practice that you cannot read your way to.

If you have done an introductory course and want to go further: read the forecast daily through the season, even on days you are not going out. It builds calibration. After a whole season of daily reading, you know how the season has developed in an area in a way no article can convey.

For longer ski tours: link the forecast to a concrete route choice using a map app with slope-angle indication, and build up to topptur once you have the system in place. Skins and randonnée gear covers the practical equipment.

Learn more

Text: Snuitide (2026).