Avalanche glossary
Weather
The essential factors wind, precipitation and temperature
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Wind
The wind is known as the architect of the avalanche, because it causes the formation of snow slabs through snow drifts of freshly fallen snow or older ones. Thereby snow particles are crushed, conveyed and deposited as drift snow.
Against the wind the hoar frost grows as also the tips of the sastrugi. Snow cornices in contrast grow in the wind direction, similar to the cometary tail, which looms behind obstacles. Dunes and wind craters are clear signs of wind activity.
The direction of surface winds is dependent on the prevailing wind direction of the respective weather conditions, the wind force and the terrain relief. Drift snow is found not only in lee areas close to the ridge from windward to leeward, but also in gullies and shallow basins by the wind blowing parallel to the slope.
Precipitation
In the assessment of an avalanche threat, the amount of precipitation in combination with wind, temperature and the existing old snowpack constitute a central factor. Whether the amount of snow in a snowfall period (1-3 days) is to be assessed as critical or rather unproblematic, depends on the above conditions during and immediately after the snowfall. An amount of 10-20 cm of fresh snow, fallen with strong wind exposure at low temperatures on an old layer of melt-freeze crust can have a highly critical impact. On the other hand, fresh snowfall of 30 cm fallen on a wet layer with no wind and at a temperature of around 0°C at the beginning constitutes no significant increase in risk. Altitude and temperature profile during the precipitation have different effects on the avalanche situation, so this must be critically assessed.
Temperature
One of the basic conditions to be observed during and after the snowfall is the temperature. Cold, hot air and sunlight considerably affect the transformation processes in the snowpack and thus also the avalanche situation.
Considerable warming leads to very critical situations, but its impact can be well assessed.
Slow, moderate warming promotes the settling of the snowpack and therewith the binding between the layers.
Warming during the day and cooling at night causes an ideal solidification of the snowpack, but an aggravation of the avalanche situation must be taken into account due to solar radiation during the day from E to W.
Cold preserves existing hazards and delays the settlement.
Persistent, severe cold promotes the formation of floating snow (ball bearing effect) and surface hoar (covered by a critical weak layer of snow), resulting in a worsening of the situation.
Considerable warming
--
Slow, moderate warming
+
Warming during the day, cooling at night
++
Cold
-
Persistent, severe cold
--
The wind is known as the architect of the avalanche, because it causes the formation of snow slabs through snow drifts of freshly fallen snow or older ones. Thereby snow particles are crushed, conveyed and deposited as drift snow.
Against the wind the hoar frost grows as also the tips of the sastrugi. Snow cornices in contrast grow in the wind direction, similar to the cometary tail, which looms behind obstacles. Dunes and wind craters are clear signs of wind activity.
The direction of surface winds is dependent on the prevailing wind direction of the respective weather conditions, the wind force and the terrain relief. Drift snow is found not only in lee areas close to the ridge from windward to leeward, but also in gullies and shallow basins by the wind blowing parallel to the slope.
Precipitation
In the assessment of an avalanche threat, the amount of precipitation in combination with wind, temperature and the existing old snowpack constitute a central factor. Whether the amount of snow in a snowfall period (1-3 days) is to be assessed as critical or rather unproblematic, depends on the above conditions during and immediately after the snowfall. An amount of 10-20 cm of fresh snow, fallen with strong wind exposure at low temperatures on an old layer of melt-freeze crust can have a highly critical impact. On the other hand, fresh snowfall of 30 cm fallen on a wet layer with no wind and at a temperature of around 0°C at the beginning constitutes no significant increase in risk. Altitude and temperature profile during the precipitation have different effects on the avalanche situation, so this must be critically assessed.
Temperature
One of the basic conditions to be observed during and after the snowfall is the temperature. Cold, hot air and sunlight considerably affect the transformation processes in the snowpack and thus also the avalanche situation.
Considerable warming leads to very critical situations, but its impact can be well assessed.
Slow, moderate warming promotes the settling of the snowpack and therewith the binding between the layers.
Warming during the day and cooling at night causes an ideal solidification of the snowpack, but an aggravation of the avalanche situation must be taken into account due to solar radiation during the day from E to W.
Cold preserves existing hazards and delays the settlement.
Persistent, severe cold promotes the formation of floating snow (ball bearing effect) and surface hoar (covered by a critical weak layer of snow), resulting in a worsening of the situation.
Considerable warming
--
Slow, moderate warming
+
Warming during the day, cooling at night
++
Cold
-
Persistent, severe cold
--
