SnowFlurry 17 2016/17 | The altitude delimitations in the situation report.

Drift snow problem & Fresh snow problem

The prevalence of a drift snow problem depends on the one hand on the wind force, the amount of transportable snow on the ground and the amount of fresh snow. On the other hand, it depends on the temperature: the colder it is, the easier it is to disturb drift snow packs (especially when they are fresh). It can happen that fresh drift snow packs are relatively difficult to disturb due to high temperatures. As a result, the height separation increases even though the wind speed is higher than the transport strength even at lower altitudes. The delineation is primarily based on station data in combination with knowledge of the current snow surface conditions. The situation is quite similar for the fresh snow problem. With both of these avalanche problems, the avalanche danger usually increases continuously with increasing altitude, so it becomes more dangerous as you go up.

Wet snow problem

The vertical extent of the wet snow problem can be predicted on the basis of the air temperature and the snowpack structure: Where is the snowpack already isothermal (has the same temperature from the ground to the surface, in this case 0°C - here the temperature measurement is just as important as the layer profile) or where does it still have temperature reserves, i.e. are there still layers with a snow temperature of a few degrees below zero? If it is isothermal, how wet is the snowpack at what altitude? This again requires weather stations, temperature forecasts and field surveys on the condition of the old snow cover. The risk of avalanches normally decreases with increasing altitude due to the colder temperatures. In the classic spring situation, the danger situation first arises at low altitudes before it calms down here due to thawing or several melting/freezing cycles. The danger zone then rises continuously with periods of fine weather and warm temperatures and increasingly affects shaded slopes. The hazard potential also shows a flowing transition in the terrain.

Summary

Avalanche problems are narrowed down using all methods - not least because they often occur in combination. In the case of drifting snow and fresh snow, the focus remains on station data and weather forecasts. In the case of wet snow problems, snowpack investigations play a major role alongside these, whereby the focus here is more on the snow temperature, less on the layer profile and even less on stability tests. In the case of old snow problems, snowpack tests are the be-all and end-all when it comes to both formation and decay: here, the focus is on the layer profile, i.e. layer hardness, grain shapes and sizes, and primarily on the load test. In this case, the temperature measurement is quite useful for estimating the progressive build-up transformation, but is of little help with regard to the current status.

The common factor here is the integration into the overall situation with reflexive analysis and process thinking. This creates an overall picture that can classify the problems according to severity, region, altitude, exposure and slope steepness.

Note: The significance of the altitude data for the distribution of avalanche problems is relatively high. The problem areas can be narrowed down very precisely in many - but not all - cases, particularly with regard to the distribution of weak layers that have been transformed by building up.