Radar products for hydrological applications in the UK

High-resolution precipitation estimates from weather radar and radar-based precipitation forecasts are key inputs to hydrological applications and, in particular, to flood forecasting models. This paper examines the processes applied to the radar-measured reflectivity data from the UK weather radar network in order to derive products useful for hydrological applications. This starts with the quality control of the reflectivity scan data then looks at processes to convert the measured reflectivity into estimates of precipitation rate close to the ground. The approaches applied operationally at the UK Meteorological Office are compared with other operational approaches. In order to use radar data for hydrological applications, it is important to understand the likely error characteristics of the precipitation estimates. Two different approaches to representing this uncertainty are outlined. The first considers a quality index, formed by combining a number of different components, representing different sources of error, multiplicatively. The second approach considers the generation of ensemble precipitation estimates which represent the likely spread of errors. The use of the precipitation estimates in generating short-period probabilistic precipitation forecasts is discussed. The methodology adopted in the short-term ensemble prediction system is outlined. Characteristics of these radar products are illustrated with a precipitation event.