Central Prealps
Melchtal
Hard-to-read day. Considerable, with new snow, persistent weak layers and gliding snow in play — you can read the surface problem; the buried one sets the consequence.
Day Risk Profile
Avalanche Problems
New snow + Persistent weak layers
3=
Field notes
New snow
Easy to spot - the snow is fresh. Look at recent avalanche activity in similar terrain, and pay attention to how much new snow has fallen in the last three days. Critical loading depends on temperature, wind, and what was on the surface before the storm. SLF advises waiting until the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has had time to bond before committing to steep terrain in fresh snow.
Persistent weak layers
Persistent Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary are very challenging to recognise. Distinctive noise (resembling a “whumpf” sound) occurring when a weak layer beneath a slab collapses. The air of the weak layer is forced outside the snowpack, with the resulting whumpf sound being heard. The sound usually indicates an unstable situation and can be accompanied by surface cracking. A whumpf is a clear avalanche alert.EAWS glossary sounds and shooting cracks are typical when present, but you can have a serious weak layer with no warning signs at the surface. Knowledge of how the Snow deposited on the ground in a multiplicity of layers.EAWS glossary has evolved is essential. SLF's travel advice is direct: travel conservatively, avoid terrain where the consequences of being caught are large, and treat the history of weather and snow as more important than what you can see today. Read the full bulletin.
Gliding snow
2
Field notes
Almost impossible to predict precisely, even when the warning signs are visible. A crack visible on the snowpack surface formed by snow-gliding on steep, and particularly grass-covered slopes. Areas below slopes with visible glide cracks should be avoided whenever possible due to threat of gliding sluffs or avalanches.EAWS glossary — gaps that open in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary down to the ground — are often precursors to release, but they don't tell you when. A glide avalanche can release minutes after the cracks appear, or weeks later, or not at all. Some release without any visible warning. Avoid lingering anywhere near glide cracks: above them, alongside them, or below in the runout.
Snowpack & Weather
Snowpack
In the north, Tuesday's large volumes of fresh and drifted snow are gradually stabilizing. In some places, however, the fresh snow from recent days is lying on faceted Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary and in some cases also buried Transparent, frequently flat crystals forming on the snowpack when moist air settles on the surface. It forms most often during cold, clear, humid nights. Once it is blanketed by fresh fallen snow, surface hoar is one of the most critical weak layer. See also: www.snowcrystals.itEAWS glossary, particularly on shady slopes. In these weak layers, avalanches can be triggered, which may occasionally become large.
In the inneralpine regions of Valais and especially Grisons, Snowpack layer in which the crystals are poorly bonded and the layer has the potential to fail. Typical crystals in dry weak layers causing avalanches are : precipitation particles; surface hoar; faceted crystals; hollow crystals; graupel. Generally >1mm in size, loose grains with few bonds Wet weak layers can be formed by all snow crystal/grain types.EAWS glossary deeper in the Snow deposited on the ground in a multiplicity of layers.EAWS glossary are also still prone to triggering in some places. Isolated avalanches may also be triggered in near-ground weak layers.
Weather review for Wednesday
Conditions were quite sunny in the west and south after a mostly clear night, while the east saw some sunny intervals.
Fresh snow
-
Temperature
At midday at 2000 m, between -8 °C in the north and -4 °C in the south
Wind
Northeasterly
- strong at night, increasing to storm-force at times
- easing to mostly moderate during the day
Weather forecast to Thursday
After a generally clear night, conditions will be quite sunny in the west and south, while the east will see some sunny intervals. Cloud will build up further in the afternoon, but it will remain mostly dry.
Fresh snow
-
Temperature
At midday at 2000 m, around -4 °C in the north and 0 °C in the south
Wind
- Easing overnight to mainly light to moderate northeasterly
- Increasingly moderate northerly during the day, strong in the afternoon on the main Alpine ridge
Outlook to Saturday
In the west and south, the nights will be mostly clear, and conditions will be mostly sunny during the daytime. In the east the nights will be partly cloudy and a few snowflakes may fall locally. Friday will be mostly sunny during the day, and Saturday daytime will see some bright periods. On Friday the wind will continue to be a moderate northerly at times, easing to mostly light on Saturday. The zero degree level will be at 1600 m on Friday in the north and at 2200 m in the south. On Saturday it will rise markedly, to 2800 m in the west and south and to 2400 m in the east.
The danger of dry avalanches will decrease. The danger of wet and gliding avalanches will increase over the course of each day. On Friday, this increase will remain slight but it will be more marked on Saturday. Ski touring should be started early and finished in good time.