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<br />estimates in order to prevent ground clutter contamination (Fig. 2). Beam blockage by terrain at <br /> <br />the lowest elevation angle of 0.5 deg ranges from 10-40% over the basin, but the second <br /> <br />elevation angle is free of blockage (Fig. 3). The off-line algorithm that builds the site-unique <br /> <br />hybrid scan elevation angle data for each radar uses high resolution digital terrain height data and <br /> <br /> <br />is described in O'Bannon (1997) and Fulton et al. (1998), <br /> <br /> <br />The 0000 UTC 13 July sounding from Denver, which preceded the rainfall event by only <br /> <br /> <br />a few hours, indicated a freezing level height of 4.9 krn MSL. At the 77 krn radar range of the <br /> <br />Buffalo Creek stonn, the one-degree wide beam at the second elevation angle is below the <br /> <br />freezing level height and is therefore probably not affected appreciably by brightband <br /> <br />enhancement (Fig, 3), <br /> <br />3. Rain gauge data <br /> <br />Automated digital data from 145 rain gauges within 230 krn of FTG were collected from <br /> <br />three sources: the NWS Arkansas-Red Basin River Forecast Center (ABRFC) in Tulsa, OK, the <br /> <br />NWS Missouri Basin RFC (MBRFC) in Pleasant Hill, MO, and the Denver Urban Drainage and <br /> <br />Flood Control District (UDFCD) who maintains a gauge network primarily in the Denver <br /> <br />metropolitan area. The 56 gauges available from the first two sources include automated NWS <br /> <br />gauges as well as automated gauges from other federal agencies such as the U.S, Army Corps of <br /> <br />Engineers and the U.S. Geological Survey. They represent typical gauge data available nationally <br /> <br />for operational use by the NWS. The 88 UDFCD gauges are part of a local network whose data <br /> <br />is received by the NWS forecast office in Denver. Manual quality control of the data was <br /> <br />perfonned to remove any obviously bad reports. <br /> <br />5 <br />