Radar-Based Precipitation Processing for NWS Hydrologic Forecast Services

Abstract

The National Weather Service (NWS) runs an operational, multi-stage, precipitation processing system which determines rainfall accumulation estimates over a variety of spatial and temporal scales for use in forecasting, warning and numerical modeling applications and for dissemination to the general public. The primary input data to this system are radar reflectivity factor returns provided by the Weather Surveillance Radar-1988 Doppler (WSR-88D) radars of the Next Generation Weather Radar (NEXRAD) program. Since 1991 over 160 of these radars have been deployed, providing nearly contiguous coverage across most of the United States. Rain gage data are also incorporated at various stages of the system, principally to provide calibration of radar rainfall estimates. As the processing proceeds across NWS venues from a local to a regional to a national level, numerous quality control operations are performed, radar rainfall data are composited together spatially (mosaicked), and a wide variety of products are generated including alphanumeric, graphics-display, and high-resolution, digital-data. The products, which are updated as often as every five minutes, provide guidance to forecasters and input to hydrologic and other numerical models. In some instances, they are made available to users outside the Weather Service, as well.