Please note that this product is experimental and is not operationally supported, meaning that there may be some gaps in the availability on the EFAS web interface due to outages.
The Radar Coverage product shows the area covered by the OPERA pan-European radar composite. The product is computed once per hour to show the latest available observations, please see the instructions at the bottom of this page for guidance on loading this product into the EFAS web interface. The radar data are used to derive rainfall accumulation nowcasts which are input to the radar-based flash flood products, and therefore users are encouraged to use the radar coverage product to help interpret the radar-based flash flood impact products. For example, the urban flash flood products are not available in areas outside of the radar coverage. River flash flood impacts are forecasted in areas outside of the radar coverage using forecasts from the ECMWF NWP, which are expected to be less accurate in predicting extreme rainfall associated with convective conditions, furthermore the ECMWF NWP forecasts are only updated 4 times per day rather than every hour. We recommend to exercise caution when interpreting the river flash flood impact products in areas outside of the valid radar coverage.
Figure 1. Radar coverage product shown on the EFAS web interface for the 24th February 2025 at 12 UTC. The darker grey shades show where no radar data were available.
Methodology
The radar data which are provided at a given hour include a mask, which shows locations within the European domain (Figure 1) with no valid data from the radar observation network. Radar data can be missing for reasons including: the area not being covered by the existing radar network, the radar at a particular location being offline at that particular time, or errors with the data provided by a particular radar location. To prevent discontinuities at the edge of the radar coverage, the inverse of a hyperbolic tangent weighting function is applied, this produces a smooth transition from areas with valid radar coverage to those without radar coverage (shown in grey in Figure 1).
Layer Usage on the EFAS Web Interface
When the layer is loaded into the EFAS web interface, if no other layers are loaded, it will by default load for the latest 00 or 12 UTC forecast for which the main hydrological EFAS forecasts are available. If the user wishes to view the layer for a hourly forecast, i.e. one other than 00 or 12 UTC, the user must do the following (these instructions are also given on Figure 1):
- Remove the Radar coverage layer from the legend window
- Load the Radar-based river flash flood impact 0-6h Catchment Summary layer
- Select the forecast date of interest
- Load the Radar-based coverage layer