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Abstract. National Meteorological and Hydrological Services (NMHSs) increase their efforts to deliver impactbased weather forecasts and warnings. At the same time, a desired increase in cost-efficiency prompts these services to automatize their weather station networks and to reduce the number of human observers, which leads to a lack of "ground truth" information about weather phenomena and their impact. A possible alternative is to encourage the general public to submit weather observations, which may include crucial information especially in high-impact situations.We wish to provide an overview of the state and properties of existing collaborations between NMHSs and voluntary weather observers or storm spotters across Europe. For that purpose, we performed a survey among 30 European NMHSs, from which 22 NMHSs returned our questionnaire. This study summarizes the most important findings and evaluates the use of "crowdsourced" information. 86 % of the surveyed NMHSs utilize information provided by the general public, 50 % have established official collaborations with spotter groups, and 18 % have formalized them. The observations are most commonly used for a real-time improvement of severe weather warnings, their verification, and an establishment of a climatology of severe weather events.The importance of these volunteered weather and impact observations has strongly risen over the past decade. We expect that this trend will continue and that storm spotters will become an essential part in severe weather warning, like they have been for decades in the United States of America. A rising number of incoming reports implies that quality management will become an increasing issue, and we finally discuss an idea how to handle this challenge.

In the course of one year the working group for quality criteria of the Citizen Science Network Austria developed a catalogue of criteria for citizen science projectson the platform Österreich forscht. From this catalogue questions were generated, which should help the project leaders of projects in Austria to fulfil the criteria. By answering the questions, important topics are addressed during the implementation of a project and can thus also be considered by the project management. On the other hand, the answers help potential project participants to make an informed decision about participation on the basis of the information presented.Project leaders receive this catalogue of questions and send the answers back to Österreich forscht. The platform coordinators read the answers, consult with the Working Group for Quality Criteria if necessary and contact the project leaders in case of ambiguities for clarification and possible assistance. The aim of this processis not to exclude individual projects, but to jointly ensure the quality of the citizen science characteristics of the projects and eventually even increase them. An open dialogue and exchange and a respectful interaction between all participants is the prerequisite for this.

Abstract. Information from voluntary storm spotters has been an increasingly important part for the severe weather warning process at the Zentralanstalt für Meteorologie and Geodynamik (ZAMG), Austria's National Weather Service, for almost 15 years. In 2010 a collaboration was formalized and an annual training was established to educate voluntary observers into “Trusted Spotters”. The return of this investment is a higher credibility of their observations after these spotters have undergone a basic meteorological training and have become aware of their responsibility. The European Severe Storms Laboratory (ESSL) was included to this collaboration to adopt their successful quality control system of severe weather reports, which is employed in the European Severe Weather Database ESWD. That way, reports from Trusted Spotters automatically obtain a higher quality flag, which enables a faster processing by forecasters on duty for severe weather warnings, when time is a critical issue. The concept of combining training for voluntary storm spotters and a thorough quality management was recognized as a “Best Practice Model” by the European Meteorological Society. We propose to apply this concept also in other European countries and present its advancement into an even broader, pan-European approach. The European Weather Observer app EWOB, recently released by ESSL, provides a novel and easy-to-handle tool to submit weather and respective impact observations. We promote its use to provide better data and information for a further real-time improvement of severe weather warnings.