Insights from operationalizing a rain warning proposal algorithm for forecasters at MeteoSwiss

Issuing warnings for severe weather events is a core duty of national weather services to help protect society and critical infrastructure. At MeteoSwiss, forecasters carry the responsibility to issue such warnings for large-area rain events. To support them in this task, they are provided with a range of targeted automatized severe weather products.

In this contribution, we focus on a newly available rain warning proposal product that we operationalized at the end of 2025. Our algorithm summarizes noisy severe weather information from ensemble forecasts into smooth large-scale rain warning proposals and delivers them to our forecasters once a day in the morning, as a basis for their assessment of the warning situation. The algorithm was developed in close collaboration with forecasters to ensure that the resulting warning proposals align with their operational needs. Each warning proposal consists of an estimate of the warning level, the affected regions, the affected time span, and the expected precipitation amount. The forecasters can choose to accept, modify, or reject the proposals. If they accept or modify a proposal, they need to add some additional text information, regarding e.g., potential impacts and behavior recommendations, to the proposal before issuing it as an official warning.

Here, we will share our lessons learned from the operationalization process and provide an overview of the forecasters’ feedback we gathered and its consequences for our continued algorithm developments. Additionally, we will highlight emerging potential application areas of our warning proposal algorithm beyond its primary use, ranging from warning verification to numerical weather prediction (NWP) model development and climate change assessments.