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Danger levels rain

Rain is the most common form of liquid precipitation from clouds, and develops as a result of small, suspended cloud droplets growing into larger drops of water, which then fall to earth because of their weight.

Danger level 5 (very severe danger)
Effects
  • Flooding, even in areas which are not usually prone to flooding;
  • Extreme swelling of streams, waterfalls or normally dry ditches, even in areas which are normally at low risk;
  • Failure of drainage and sewer systems and flood protection barriers;
  • Flooding of underpasses, underground garages and cellars/basements;
  • Massive disruption to road and rail traffic;
  • High likelihood of landslides on sloping terrain and mudslides.
Behaviour

Information on recommended action can be found here:  What to do during heavy rainfall

Description of
measurement and prognostic values
  • Sustained rainfall north of the Alps and in the Alps: >120 mm/24 h, > 150 mm/48 h, >170 mm/72 h
  • Sustained rainfall south of the Alps and in Simplon: >160 mm/24 h, > 200 mm/48 h, >240 mm/72 h
  • Sustained rainfall in Verbano, Valle Maggia: >250 mm/24 h, > 300 mm/48 h, > 350 mm/72 h
Danger level 4 (severe danger)
Effects
  • Potential for rivers to overflow onto floodplains and flood zones as well as around lake shores.
  • Heavily swollen streams, waterfalls and normally dry ditches, and flooding of cave systems;
  • Potential for localised landslides on steeply sloping terrain;
  • Failure of drainage and sewer systems;
  • Flooding of underpasses, underground garages and cellars/basements;
  • Disruption to road and rail traffic.
Behaviour

Information on recommended action can be found here:  What to do during heavy rainfall

Description of measurement and prognostic values

  • Sustained rainfall north of the Alps and in the Alps: 80-120 mm/24h, 110-150 mm/48h, 130-170 mm 72h
  • Sustained rainfall south of the Alps and in Simplon: 130-160 mm/24 h, 160-200 mm/48 h, 200-240 mm/72 h
  • Sustained rainfall in Verbano, Valle Maggia: 200-250 mm/24 h, 250-300 mm/48 h, 300-350 mm/72 h
Danger level 3 (significant danger)
Effects
  • Swelling of streams, waterfalls and normally dry ditches, and flooding of exposed cave systems;
  • Disruption to road traffic on exposed stretches
Behaviour

Information on recommended action can be found here:  What to do during heavy rainfall

Description of measurement and prognostic values

  • Sustained rainfall north of the Alps and in the Alps: 50-80 mm/ 24 h, 80-110 mm/48 h, 100-130 mm/72 h
  • Sustained rainfall south of the Alps and in Simplon: 100-130 mm/24 h, 130-160 mm/48 h, 160-200 mm/72 h
  • Sustained rainfall in Verbano, Valle Maggia: 150-200 mm/24 h, 200-250 mm/48 h, 250-300 mm/72 h

 

Danger level 2 (moderate danger)
Effects

Local swelling of streams or local flooding possible in areas where the ground is already saturated

Behaviour

Keep an eye on local weather developments, and act appropriately, according to the information you  receive on the conditions;

Description of measurement and prognostic values

  • Sustained rainfall north of the Alps and in the Alps: 30-50 mm/24 h
  • Sustained rainfall south of the Alps and in Simplon: 70-100 mm/24 h
  • Sustained rainfall in Verbano, Valle Maggia: 100-150 mm/24 h

Notes:

These warnings are primarily used for widespread precipitation (also potentially in combination with a thunderstorm in the summer).

Please note: the warning threshold values differ for north and south of the Alps within the same warning category!

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