TITLE: NWS ABRFC Stage III gridded WSR-88D Daily Data CONTACTS: Steve Williams UCAR/JOSS P.O. Box 3000 Boulder CO 80307-3000 email: sfw@ucar.edu phone: 303-497-8987 1.0 DATA SET OVERVIEW This data set contains daily resolution 4 km by 4 km gridded precipitation fields produced by the National Oceanic and Atmospheric Administration (NOAA) Arkansas-Red Basin River Forecast Center (ABRFC). The fields are a combination of radar derived estimates and raingage reports of precipitation. The products cover all of Oklahoma, most of Kansas, southeastern Colorado, eastern New Mexico, northern Texas, and western Missouri and Arkansas. Data cover the period from 01 June to 31 July 2002. The data are in netCDF format. 2.0 INSTRUMENT DESCRIPTION No information. 3.0 DATA COLLECTION AND PROCESSING These radar-derived precipitation images are created once per day (in the morning) for the 24 hours from 12z the previous day to 12z the current day. They are created by adding the 24 one-hour precipitation totals that make up that time-frame. The ABRFC hydrologic day runs from 12z to 12z, not midnight to midnight or 00z to 00z. Every hour (usually between half past and the top of the hour), the HAS (hydrometeorological analysis and support) forecaster creates a gridded (4 km x 4 km) precipitation field. This field is a combination of both WSR-88D Nexrad radar precipitation estimates and raingauge reports. These gridded fields are used as input into the ABRFC's hydrologic model. The ABRFC has two methods of producing gridded precipitation fields using radar data and rain gauge reports. These are P1 and Stage III. Both use the same basic input: the hourly digital precipitation product (HDP) computed by each radar within the ABRFC's area, and hourly rain gauge reports (usually at automated reporting sites). Both also use Hydrologic Rainfall Analysis Project or HRAP grid, a 4km x 4km grid. The following are two simplistic descriptions. P1 Methodology: Every hour, a mosaic of all the HDPs is created by combining them in one product that covers the entire ABRFC basin. Where radars overlap, the average value is taken. Also each hour, a collection of all reporting rainfall amounts from gauge sites is created. A irregular triangulated grid field is created using the locations of the gauge sites. The radar mosaic is overlayed on this triangulated grid and a 'bias' field is created based on the difference between the radar value and the gauge value. Where there is no gauge site, a 'bias' is computed using the triangular grid and the distance from the nearest gauge sites. The resultant bias field is then used to create the final precipitation product. P1 works well when there are numerous gauge sites available, otherwise the fields tend to get spread out too much based on the large triangular grids created. P1 was designed after a similar method of daily precipitation processing created by the Tulsa District Corps of Engineers. StageIII Methodology: StageIII was created by the at the Office of Hydrology's Hydrologic Research Lab(HRL). For each radar HDP field, the differences between the gauge values and the corresponding HDP grid values are combined to create a single bias for the entire radar field. This bias is then used to compute a new 'multi-sensor' precipitation field for each radar. These multi-sensor fields are then mosaicked into a total basin precipitation field. StageIII tends to work very well in midwestern convective situations. For more information, visit HRL's Hydrometeorological Analysis Group (HAG). UCAR/JOSS conducted no processing or quality control on these data. 4.0 DATA FORMAT AND FILE NAMING 4.1 Data Format These data are in network Common Data Form (netCDF) format. For information on netCDF see: http://www.unidata.ucar.edu/packages/netcdf/ 4.2 File Naming conventions 0530200312z.nc where: 05 is the month (May) 30 is the day 2003 is the year 12z is the ending time of the precipitation 5.0 DATA REMARKS None. 6.0 REFERNCES ABRFC Home Page: http://www.srh.noaa.gov/abrfc/