Gotthard area
Uri Rot Stock
Day Risk Profile
Avalanche Problems
Wind slab + Persistent weak layers
2=
Field notes
Wind slab
Look for fresh snow deposits on Slope facing downwind/ wind sheltered aspect. Snow deposits can attain several times average snow depth.EAWS glossary, in Usually a steep, elongated, eroded trench; typically prone to snowdrift accumulation.EAWS glossary and Rounded or elongated concavity; typically tending to accumulate snowdrift.EAWS glossary, and behind ridgelines and abrupt changes in terrain — these are where the wind has loaded the snow into slabs that are easy to trigger. Recent avalanches, shooting cracks under your weight, and 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 are clear confirmations of the problem. The safest move is to avoid wind-loaded terrain entirely. NB wind signs alone don't always mean an avalanche problem exists, and the age of drifted snow is hard to judge.
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.
Snowpack & Weather
Snowpack
Fresh snow and westerly winds are producing snowdrift accumulations in the west and north, the largest forming in the west, where the most snow is falling.
Snow deposited on the ground in a multiplicity of layers.EAWS glossary structure is unfavourable in many locations in southern Valais, Ticino and Grisons, where this week's fresh and drifted snow is lying on an unfavourable Snow layers deposited from earlier precipitation, prior to fresh fallen snow. Old snow layers consist of metamorphosed snow crystals.EAWS glossary with pronounced 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. Reports of 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 avalanches triggered by human activity, some from a distance, are still being received from these regions. Snowpack structure is somewhat more favourable on the northern flank of the Alps and in northern Valais, but there are weak layers deeper in the snowpack in these regions too. These may still be triggered, especially where there is little snow and at transitions from a deep to shallow snowpack.
Weather review for Thursday
A light sprinkling of snow fell in the south during the night. Conditions were mostly sunny during the day.
Fresh snow
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Temperature
At midday at 2000 m, around -1°C
Wind
Mostly light at night, increasingly moderate southwesterly in the west during the day
Weather forecast to Friday
Snow will fall during the night in the west and south. There will be widespread snowfall in the north, Valais and Grisons during the day, while conditions will be very sunny in the south. The snowfall level will be around 1300 m.
Fresh snow
From Thursday evening to Friday afternoon above approximately 1500 m:
- extreme west and northern Lower Valais: 15 to 30 cm
- western Jura, western part of the northern flank of the Alps apart from the Prealps, rest of northern Valais, rest of Lower Valais: 10 to 20 cm
- elsewhere a widespread 5 to 10 cm
Temperature
At midday at 2000 m, around -1°C
Wind
- Strong foehn wind for a time at night on the Main Alpine Ridge and north of there
- During the day, moderate to strong westerly in the north; light to moderate northwesterly in the south
Outlook for Saturday and Sunday
Overnight to Saturday, a little snow will continue to fall in the north above 1300 m. Conditions during the day will be very sunny with sunny conditions continuing until early on Sunday. In the afternoon, clouds will gather from the west and south. There will be a mostly light wind on both days.
Avalanche risk will decrease but only very slowly in southern Valais, Ticino and Grisons due to the distinct and 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.