The nowcast, forecast and verification of very local weather effects, like wind gusts, fog or hail storms, is a challenging issue in meteorology. Although enormous progress has been made on the side of the NWP modelling, forecasting the exact locations of these phenomena still remains a challenge. Moreover, the forecasts of these phenomena are often difficult to verify since there is a lack of ground truth data: in many cases only fragmentary observations are available e.g. through our climatological network or through (social or conventional) media.

In particular, there is a lack of ground observations of precipitation type and related quantities like hailstone dimensions and snow depth. Hydrometeor classification schemes based on dual-pol radar data can contribute to this verification, but these algorithms suffer from the limitation that they can only provide information on hydrometeor type at the measurement height of the radar. In recent years it became clear that enabling citizens to fill these observational gaps is a particularly effective approach.

Currently our section runs two distict systems in which citizens are the providers of this additional meteorological information.

The RMI is collecting data from privately owned weather stations through the international WOW network (Weather Observations Website). This network was launched in 2011 by the UK MetOffice and started as an observations sharing platform, where weather enthusiasts, schools and organisations can all upload and share their latest weather observations. WOW evolved from a national (UK) initiative to a global network of more than 10,000 privately owned weather stations. Meanwhile also BOM (Australia), MetService (New Zealand), KNMI (the Netherlands), Met Éireann (Ireland) and SMHI (Sweden) have joined WOW. In 2017, the RMI joined the network with the launch of WOW-BE and a growing number of personal weather stations in Belgium are being connected to the platform.

Another promising approach to obtain very local weather information is the collection of citizen weather reports through smartphone apps. In August 2019, the RMI added such a reporting feature in its existing smartphone app. The user of the RMI app is enabled to send a meteorological observation with a few simple taps on his device, through a clean and attractive interface. The reporting feature is much more successful than was anticipated before launch, and around 900,000 reports are collected each year (on a total population of 11.5 million inhabitants in Belgium).

While this information collection strategy also suffers from several weaknesses like certain quality issues or a strong population density bias, it has become a very important additional data source for both the operations and the research at the RMI. In the Radar and Lighnting Detection section, we are responsible for the general design and the pre-processing of the incoming data, including an automatic on-the-fly sanity check of every incoming observation. In addition, the citizen reports database is used to conduct studies in the field of precipitation type, mainly hail and snow detection.