Problems of calibration of weather radar are addressed. Methods have been developed aimed at how to process the radar-based precipitation data for hydrology applications. Aggregated data (10x10 km) are suggested to be reasonably sufficient for that aim. Basic properties of precipitation fields are examined: (1) spatial coverages and areal reduction factor, (2) conditional frequency distribution function of “at-cell” rain rates by specified spatially averaged rates and, (3) spatial structural function (variogram). Examples of data processing and analysis are given to expound upon the ideas of how to describe precipitation patterns. For flood forecasting, a procedure is proffered to reveal those rain rates exceeding threshold which is correlated with antecedent soil moisture content on a small (2000 km²) river basin.