The NEXRAD Rainfall Estimation Processing System: A radar tool to improve rainfall estimation across the Tennessee River Valley

An operational system using the NEXRAD network to estimate rainfall across the Tennessee Valley, independent of rain gauge input, has been developed for implementation by a regional water management organization, the Tennessee Valley Authority (TVA). The Advanced Radar for Meteorological and Operational Research (ARMOR), which is a dual-polarimetric C-band Doppler radar located in Huntsville, AL, was used as a demonstration to the TVA of the future rainfall estimation capability of NEXRADs, which are slated to be upgraded to dual-polarimetry. The ARMOR Rainfall Estimation Processing System (AREPS) was developed and it provided hourly rainfall data across the Central Tennessee Valley to the TVA. The demonstration project with AREPS successfully proved that radar-derived hourly rainfall estimation is not only possible but that it also compares rather well to rain gauge measurements. In order to expand the radar coverage across the rest of the Tennessee Valley, the NEXRAD Rainfall Estimation Processing System (NREPS) was developed. NREPS employs several WSR-88Ds and quality control methods to derive hourly rainfall accumulation across the Tennessee Valley. Although NREPS does not currently use dual-polarimetry to estimate rainfall (algorithms will be ported over from AREPS once the NEXRADs are upgraded), initial comparisons with rain gauge derived rainfall indicate that NREPS should enable TVA to reduce its reliance on, and costs associated with, coarse rain gauge networks that do not adequately cover individual sub-basins in the watershed.