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Danger levels heat wave

Our perception of heat is affected by the following meteorological parameters: air temperature, radiation from the sun, relative air humidity, and wind.

  • Heat = the perceived discomfort as a result of excessive air temperature
  • Heatwave = a period of extreme heat stress, which can endanger human health

Since heat is better tolerated at low relative air humidity, the heat warnings from MeteoSwiss are based on a calculated value that combines temperature and relative humidity: the so-called heat index.

In Switzerland, heatwaves usually occur in conjunction with high-pressure conditions and a south to south-westerly flow of air, so that warm, dry air is pushed toward the Alpine region.

Danger level 1 (no or minor danger)

Heat warnings are issued only for levels 3 and 4.

Danger level 2 (moderate danger)

Heat warnings are issued only for levels 3 and 4.

Danger level 3 (considerable danger)

Effects

  • Risk of circulatory complaints
  • Physical discomfort

Behaviour

For information on recommended action, see What to do during a heatwave or the Swiss Federal Office for Public Health (BAG) website.

Description of measurement and prognostic values

  • Heat Index HI > 90
  • Min. 3 days
  • Heatwave with temperatures remaining over the threshold value for three days or more

Danger level 4 (high danger)

Effects

  • Risk of circulatory complaints
  • Physical discomfort

Behaviour

For information on recommended action, see What to do during a heatwave or the Swiss Federal Office for Public Health (BAG) website.

Description of measurement and prognostic values

  • Heat Index HI > 93
  • Min. 5 days
  • Heatwave with temperatures remaining over the threshold value for five days or more

Danger level 5 (very high danger)

Heat warnings are only issued for categories 3 and 4, since a heatwave more extreme than this is very unlikely to occur in these latitudes.

Notes

As mentioned above, heat warnings are based on the so-called heat index (HI). This denotes the perceived temperature, which is calculated by combining the actual temperature with the relative air humidity.

Table with dew point and temperature to determine the Heat Index
Table with dew point and temperature to determine the Heat Index
Table with relative humidity and temperature to determine the Heat Index
Table with relative humidity and temperature to determine the Heat Index