Calibration of the X-band LAWR (Local Area Weather Radar) is traditionally based on an assumed linear relation between the LAWR radar output and the rainfall intensity. However, closer inspection of the data reveal that the validity of this linear assumption is doubtful. Previous studies of this type of weather radar have also illustrated that the radar commonly has difficulties in estimating high rain rates. Therefore, a new radar–rainfall transformation model and a calibration method have been developed. The new method is based on nonlinear assumptions and is aimed at describing the whole range of rain intensities in a more comprehensive way for the LAWR system. The new proposed calibration method improves the LAWR QPE (quantitative precipitation estimate) accuracy by reducing bias and describing the temporal dynamics better for the vast majority of the observed rainfall. However, in heavy rainfall, the LAWR system still faces significant challenges in measuring the peak intensities accurately.