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 5 (very severe 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.

Danger level 4 (severe danger)
Effects 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 (german).
Description of
measurement and prognostic values
  • Heat Index HI > 93
  • Min. 5 days
  • Extreme heatwave, with temperatures remaining over the threshold value for five days or more
Danger level 3 (significant danger)
Effects 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 (german).
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

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.