If bad weather is imminent, the MeteoSwiss weather centre alerts the Emergency Organisation EO Met. EO consists of specialists from the MeteoSwiss weather, climate and communications departments. In more severe events (generally level 4 and above on the five-point scale, signifying high danger), the specialist natural hazards task force is called into action in case there is a threat of several simultaneous hazards. The task force consists of members of the various specialist agencies, which also includes the Emergency Organisation of MeteoSwiss. The combined forces of the specialist agencies in the task force coordinate their warnings and issue joint natural hazard bulletins and news releases, which are published on the Natural Hazards Portal.
The joint warnings, bulletins and reports are disseminated via the National Emergency Operations Centre. These serve as a decision-making basis for the authorities (cantonal executive staff, emergency organisations and natural hazard specialists), helping them to take precautionary measures and keep the situation under control.
If a particularly serious natural hazard event on a supra-regional scale looks imminent, the authorities may issue a “single official voice” warning. This is coordinated by the relevant specialist agencies. It is recognisable as a warning issued by the Swiss government and publicised in an easily understandable and standardised format. The SRG and commercial licensed radio and television broadcasters are legally obliged to publish these warnings.
Correct warnings and false alarms
Accurately predicting the time and location of severe weather events and issuing corresponding warnings involves a great deal of work. Using high-resolution numerical forecasting models, meteorologists can assess the intensity and likelihood of the anticipated event. Potentially comparable situations from the past are also used.
On the one hand, the aim is to issue correct warnings of as many events as possible – in other words, to achieve a high hit rate. On the other hand, superfluous warnings (false alarms) should be minimised, as they incur unnecessary costs. These two aims are somewhat contradictory. When a hit rate of close to 100 percent is aimed for, the risk of issuing too many unnecessary warnings increases. On the other hand, if the aim is to keep the proportion of false alarms close to 0 percent, this will usually be associated with a lower hit rate; in this case, many events would not trigger warnings, which would result in greater damage.
A hit rate of 86% for severe weather warnings
Long experience in working with the authorities has shown that an average hit rate of at least 85 percent and a proportion of false alarms of no more than 30 percent strikes an appropriate balance. The warnings are measured against stringent threshold values. MeteoSwiss exceeds these requirements with an average hit rate of 86 percent for severe weather warnings and a 20 percent proportion of false alarms. The combination of these two key figures shows that there is an optimal cost-benefit ratio for severe weather warnings.
Warnings on the hazard map and in the MeteoSwiss app
MeteoSwiss issues warnings of wind, thunderstorms, rain, snow, icy roads, heat and frost. The warnings are issued for 159 warning regions and 51 warning subjects (lakes and airports). The authorities also receive advance warning if a significant event (warning level 3 or above) is expected with sufficient certainty (probability of 40–70%) and with a lead time of up to three days.
The hazard map shows severe weather warnings and warnings of other natural hazards such as floods, forest fires and avalanches. In the MeteoSwiss app, the user can subscribe to warnings for any location and hazard type as automatic (push) notifications. Severe weather hazards with a lower likelihood of occurrence are shown with diagonal shading over the areas affected.