The nonuniform vertical profile of reflectivity (VPR) is considered one of the most important sources of range-dependent biases in WSR-88D precipitation estimates. The Range Correction Algorithm (RCA), which has been developed by the Office of Hydrologic Development, National Weather Service, NOAA, aims to reduce such range-dependent biases. The RCA functions by estimating an areal mean VPR through volumetric scanning. This VPR is then used to estimate surface-level rainfall rate in regions where the lowest radar beam intersects the melting layer or other elevated regions where the hydrometeor distribution is different from that immediately above the surface. The RCA is currently being implemented in the Open Radar Product Generator system.

A prototype of the RCA has been operating for several months in early 2003, using real-time radar data from the Sterling, VA radar site. The purpose of this effort is to evaluate whether RCA consistently enhances the accuracy of precipitation estimates under the circumstances of real-time operations, and to develop operational guidelines for the use of RCA. We will present validation results showing the effects of range correction on 24-hour rainfall estimates verified by comparison with rain gauges in the cooperative observer network. We have found that in the winter and early spring (February-April), when precipitation is mainly from stratiform systems, the RCA consistently reduces range-dependent biases in the precipitation estimates. The improvement is realized mainly by correcting overestimates within the bright-band region and underestimates at longer ranges. However, in situations where the precipitation is a mixture of stratiform and convective types, the improvement is not as pronounced or consistent.