Snowfall amount and its related liquid equivalent precipitation amount are determined using a variety of different rain gauges. As a rule of thumb, 10 cm of fresh snowfall corresponds to 1 cm of water. As soon as snow settles on the surface, it is rapidly compressed by further snowflakes, so that typical snow covers have a density of factor 9 (powder snow) to 6 (wet snow) compared to water.
Snowfall accumulates on the surface, and can reach deposits of up to several meters in certain areas. The height of the snow cover is determined by:
- amount of snowfall;
- density of snow (usually as a function of flake structure, resulting from air temperature),
- hill slope (which reduces deposition area);
- wind transport (which may move snow away and accumulate in certain other areas);
- sliding effects;
As a result of these factors, the depth of snow cover is very difficult to estimate, and can vary substantially within a few meters distance. Our meteogram SNOW shows an average accumulated snow depth within a grid cell.
A further effect of snow cover is the phenomenon of avalanches: when snow accumulates in larger quantities on slopes, parts of this amount may suddenly slide downhill, and form large packets moving downhill at medium (10-40 km/h) to very high speeds (300 km/h) with potentially very destructive forces.
Avalanches are typically triggered in a starting zone, from a mechanical failure in the snowpack (slab avalanche) when the forces on the snow exceed its strength, and sometimes only by gradually widening (loose snow avalanche). After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they entrain more snow. If the avalanche moves fast enough, some of the snow may mix with the air, forming a powder snow avalanche.
Due to the complexity of the formation process, avalanches can not be predicted by numerical modelling.
Therefore, we do not want to offer alerts for avalanche risk: avalanches are a very localised phenomenon and the locality of the meteoblue forecast may encourage users to consider these alerts as local. This will create a risk of liability, which is beyond our capacity, and against our ethics to provide transparent information.
Avalanche warnings are provided by local and national authorities. They require a high level of expertise and also have implications for liability and insurance purposes.
We would consider offering the public avalanche warnings in the future, if they are made available by the respective national authorities, and if we find a way to clearly identify them for the area of concern, without any ambiguities.
PLEASE ALWAYS REFER TO LOCAL SOURCES FOR ASSESSMENT OF THE SNOW AND AVALANCHE SITUATION, TO ENSURE THAT YOU ARE AWARE OF THE POTENTIAL RISKS!
Snowfall indicates the total amount of fallen snow accumulated on the surface in an indicated time period. For instance, a chosen time period of the last 3 hours at 11:00 shows the total amount of fallen snow between 08:00 and 11:00, expressed as a height in centimeters (cm).
Snow depth indicates the total depth of the snow which might have accumulated over many months. It is also expressed in centimetres (cm) and is only a rough estimate. Actual snow depths vary significantly locally from the indicated values.