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The blending technique (Wong et al. 2009) is applied for the first 6 hours, and applies a phase shift and bias correction to blend radar nowcasts into NWP using a hyperbolic tangent weighting function. For lead times beyond 6 hours, the product relies only on the NWP forecasts. The displayed accumulations correspond to the forecasts obtained with the control member, and are of At each timestep this layer shows the 80th percentile of rainfall from the forecast ensemble.
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Figure 1. 80th percentile of the hourly blended precipitation ensemble forecast at 15:00 UTC on 2022-09-05
Visualising within the EFAS Webviewer
The layer can be viewed after selecting it from the Flash Flood layers tab within the EFAS webviewer. An animation slider box will appear in the bottom left of the screen and by default the data from the most recent forecast will be loaded. A drop down menu just above the animation slider box can be used to select a different forecast date and time within the past 5 days.
The buttons on the left of the animation slider can be used to step forwards and backwards in time for each timestep of the forecast. The play button will play the animation in a continuous loop. When animating each timestep, it can take a few seconds to load the next timestep, this is shown by a loading icon which appears within the animation slider which will disappear once the next timestep has been loaded.
References
Berenguer, M., Sempere-Torres, D. and Pegram, G, 2011: SBMcast - An ensemble nowcasting technique to assess the uncertainty in rainfall forecasts by Langrangian extrapolation. Journal of Hydrology, 404(3), 226-240
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