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Snow

Snow is the most common form of solid precipitation and consists of many very small ice crystals. These form at temperatures below -4 °C, and fall to earth, as long as their falling speed and the temperature and humidity below the clouds do not allow the crystals to melt or evaporate.

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Hazard category 5 (very severe hazard)
Possible impacts
  • Road and air traffic is brought to a standstill and massive disruption to rail transport
  • Falling branches or trees as a result of the weight of their snowload
  • Heavy snowload on roofs
  • Potential of breakdown of electricity supply and telephone communications network
Description of measurement and prognostic values
  • Heavy/intensive snowfall in lowland areas of German-speaking Switzerland: >50 cm/24h; >70 cm/48h; >90 cm/72h
  • Heavy/intensive snowfall in lowlands of Western Switzerland and south of the Alps: >50 cm/24h; >70 cm/48h; >90 cm/72h
  • Heavy/intensive snowfall in the mountains: >90 cm/24h; >140 cm/48h; >180 cm/72h

Hazard category 4 (severe hazard)
Possible impacts
  • Disruption to air and rail travel
  • Disruption to road traffic (delays, increased risk of accidents) to be expected owing to slippery conditions, snow drift and poor visibility
  • Falling branches or trees as a result of the weight of their snowload
  • Impassable sections of road
  • Potential of interruption of electricity supply and/or telephone network
  • Heavy snowload on roofs
Description of measurement and prognostic values
  • Heavy/intensive snowfall in lowland areas of German-speaking Switzerland: 30-50 cm/24h; 50-70 cm/48h; 70-90 cm/72h
  • Heavy/intensive snowfall in lowlands of Western Switzerland and south of the Alps: 30-50 cm/24h; 50-70 cm/48h; 70-90 cm/72h
  • Heavy/intensive snowfall in the mountains: 60-90 cm/24h; 100-140 cm/48h; 130-180 cm/72h

Hazard category 3 (significant hazard)
Possible impacts
  • Disruption to road, rail and air traffic
  • Breaking branches due to snowload
  • Worsening of road condition
Description of measurement and prognostic values
  • Heavy/intensive snowfall in lowland areas of German-speaking Switzerland: 15-30 cm/24h; 35-50 cm/48h; 50-70 cm/72h
  • Heavy/intensive snowfall in lowlands of Western Switzerland and south of the Alps: 12-30 cm/24h; 35-50 cm/48h; 50-70 cm/72h
  • Heavy/intensive snowfall in the mountains: 40-60 cm/24h; 70-100 cm/48h; 100-130 cm/72h

Hazard category 2 (moderate hazard)
Possible impacts Slippery conditions due to snow-covered roads
Description of measurement and prognostic values
  • Snowfall in lowland areas of German-speaking Switzerland: 10-15 cm/24h; 20-35 cm/48h; 30-50 cm/72h
  • Snowfall in lowlands of Western Switzerland and south of the Alps: 8-12 cm/24h; 20-35 cm/48h; 30-50 cm/72h
  • Snowfall in the mountains: 20-40 cm/24h; 35-70 cm/48h; 50-100 cm/72h

Recommendations for action

Recommendations during snow

Notes

The snowfall warnings are primarily issued for widespread precipitation.

The warning threshold values in category 2 and 3 for lowland areas differ according to region.

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