Richard A. Fulton

The WSR-88D Rainfall Algorithm

Abstract A detailed description of the operational WSR-88D rainfall estimation algorithm is presented. This algorithm, called the Precipitation Processing System, produces radar-derived rainfall products in real time for forecasters in support of the National Weather Service’s warning and forecast missions. It transforms reflectivity factor measurements into rainfall accumulations and incorporates rain gauge data to improve the radar estimates. The products are used as guidance to issue flood watches and warnings to the public and as input into numerical hydrologic and atmospheric models. The processing steps to quality control and compute the rainfall estimates are described, and the current deficiencies and future plans for improvement are discussed.

Real-Time Adjustment of Range-Dependent Biases in WSR-88D Rainfall Estimates due to Nonuniform Vertical Profile of Reflectivity

Abstract A procedure for real-time adjustment of range-dependent biases in Weather Surveillance Radar-1988 Doppler version (WSR-88D) rainfall estimates due to nonuniform vertical profile of reflectivity is proposed. Using volume-scan measurements of effective reflectivity, the procedure estimates conditional mean and variance profiles of point reflectivity in the vertical and calculates, as a function of elevation angle and slant range, a multiplicative adjustment factor to be applied to the apparent radar rain rate. As a by-product, the maximum effective coverage of radar is also delineated, outside of which radar rainfall estimates are subject to beam overshooting. To evaluate the procedure, unadjusted and adjusted radar rainfall estimates from a Pacific Northwest winter storm are examined and compared with rain gauge data.

Radar and Multisensor Precipitation Estimation Techniques in National Weather Service Hydrologic Operations

This paper describes techniques used operationally by the National Weather Service (NWS) to prepare gridded multisensor (gauge, radar, and satellite) quantitative precipitation estimates (QPEs) for input into hydrologic forecast models and decision- making systems for river forecasting, flood and flash flood warning, and other hydrologic monitoring purposes. Advanced hydrologic prediction techniques require a spatially continuous representation of the precipitation field, and remote sensor input is critical to achiev- ing this continuity. Although detailed descriptions of individual remote sensor estimation algorithms have been published, this review provides a summary of how the estimates from these various sources are merged into finished products. Emphasis is placed on the Weather Surveillance Radar-1988 Doppler (WSR-88D) Precipitation Processing System (PPS) and the Advanced Weather Interactive Processing System (AWIPS) Multisensor Precipitation Estimator (MPE) algorithms that utilize a combination of in situ rain gauges and remotely sensed measurements to provide a real-time suite of gridded radar and multisensor precipitation products. These two algorithm suites work in series to combine both computer-automated and human-interactive techniques, and they are used routinely at NWS field offices (river forecast centers (RFCs) and weather forecast offices (WFOs)) to support NWSs broader hydrologic missions. The resulting precipitation products are also available to scientists and engineers outside the NWS; a summary of charac- teristics and sources of these products is presented. DOI: 10.1061/(ASCE)HE.1943-5584.0000523.

Sensitivity of WSR-88D Rainfall Estimates to the Rain-Rate Threshold and Rain Gauge Adjustment: A Flash Flood Case Study

Abstract A strong thunderstorm produced a flash flood on the evening of 12 July 1996 in Buffalo Creek, Colorado, that caused two deaths and significant property damage. Most of the rain fell in a 1-h time period from 2000 to 2100 MDT. The performance of the WSR-88D rainfall algorithm, Precipitation Processing System, was examined in detail to determine how well it performed. In particular the sensitivity to the algorithm’s rain-rate threshold (hail cap) parameter and the performance of the gauge–radar adjustment subalgorithm on the resulting radar rainfall estimates were examined by comparison with available rain gauge data. It was determined that the WSR-88D rainfall algorithm overestimated the rainfall in general over the radar scanning domain for this event by about 60% relative to the rain gauges although the radar-derived rainfall for the flood-producing storm cell nearly matched the single gauge that sampled it. The derived rainfall over the radar scanning domain was not very sensitive to the settin...

Radar-Based Precipitation Processing for NWS Hydrologic Forecast Services

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.

GEONETCast Americas – A GEOSS Environmental Data Dissemination System Using Commercial Satellites

GEONETCast Americas is a regional contribution to a global, near-real-time, environmental data dissemination system in support of the Global Earth Observation System of Systems. It is a contribution from the United States National Oceanic and Atmospheric Administration whose goal is to enable enhanced dissemination, application, and exploitation of environmental data and products for the diverse societal benefits defined by the Group on Earth Observations, including agriculture, energy, health, climate, weather, disaster mitigation, biodiversity, water resources, and ecosystems. GEONETCast Americas serves North, Central, and South Americas beginning early in 2008 using inexpensive satellite receiver stations based on Digital Video Broadcast standards and will link with similar regional environmental data dissemination systems deployed around the world.

GEONETCast Americas: vision and plans

GEONETCast Americas is a regional contribution to a developing, global, near-real-time, environmental data dissemination system in support of the Global Earth Observation System of Systems. It will be a contribution from the United States National Oceanic and Atmospheric Administration whose goal is to enable enhanced dissemination, application, and exploitation of environmental data and products for the diverse societal benefits defined by the Group on Earth Observations, including agriculture, energy, health, climate, weather, disaster mitigation, biodiversity, water resources, and ecosystems. GEONETCast Americas will serve North, Central, and South Americas beginning late in 2007 using inexpensive satellite receiver stations based on Digital Video Broadcast standards and will link with similar regional environmental data dissemination systems deployed around the world.