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Danger levels slippery roads

Ice on the roads develops as a result of cold and wet conditions.

These warnings apply primarily to the road conditions, whilst differentiating between the following hazards:

  • Slippery conditions due to packed snow: Snow that has frozen solid on the roads (up to 4 cm thick).
  • Black ice: Wet roads which subsequently freeze over as a result of clear skies at night.
  • Icy roads: Cold or cooled precipitation (freezing rain/drizzle) that falls onto a road surface with a temperature below 0 degrees, thus freezing solid instantly.

Please note: warnings for  slippery conditions due to ice or snow are not issued foraltitudes above 800 m.

Danger levels 5 (very severe danger)
It is not possible to make a distinction for larger deposits of precipitation. Widespread ice formation on roads over a sustained period is a rare occurrence in Switzerland.
Danger levels 4 (severe danger)
Effects
  • Sudden, acute danger of skidding;
  • Road and air travel brought to a standstill;
  • Disruption to rail travel;
  • Falling branches or trees as a result of their ice load;
  • Interruption of electricity supply and/or telephone network, particularly in regions that are not easily accessible.
Behaviour

Information on recommended action can be found here:  What to do when the roads are slippery

Description of measurement and prognostic values Freezing rain: over 2 mm (total precipitation volume freezing on the ground)
Danger level 3 (significant level)
Effects
  • Sudden, acute danger of skidding
  • Icy roads to the extent of being impassable
  • Disruption to air travel
  • Branches breaking and falling as a result of their ice load
Behaviour Information on recommended action can be found here:  What to do when the roads are slippery
Description ofmeasurement and prognostic values Freezing rain: up to 2 mm
Danger level 2 (moderate danger)
Effects

Local or widespread risk of skidding

Behaviour

Information on recommended action can be found here:  What to do when the roads are slippery

Description ofmeasurement and prognostic values
  • Packed snow (less than 4 cm, road temperature of < 0 degrees)
  • Black ice (wet roads that have frozen over)
  • Icy roads (freezing rain)

Notes:

Warnings of slippery conditions due to ice or snow are not issued for altitudes above 800 m.

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