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<br />rainfall over the Buffalo Creek basin for the 14-hour time period encompassing the flash flood <br /> <br />event are shown in Fig. 14, Basin-average and basin-maximum values are computed using I-deg <br /> <br />x 2-km PPS grid cells whose centers fall within the basin. The heaviest rain occurred during the <br /> <br /> <br />one-hour period from 0200-0300 UTC, and the flash flood occurred around 0300-0400 UTC (27- <br /> <br /> <br />28 UTC in Fig. 14). According to public reports in the town, the Buffalo Creek had begun to rise <br /> <br /> <br />around 0230 UTC and was out of its banks by 0300 UTe. The river had risen about 15 feet in <br /> <br />the tov.n and had returned to [lear normal levels by midnight (0600 UTC). Light rain had passed <br /> <br />over the basin earlier in the day but had contributed only about 4 rnm (0,16 in) to the basin <br /> <br />maximum rainfall. <br /> <br />Had the rainfall rates not been capped at 51 dBl in the PPS (dashed horizontal lines in <br /> <br />Figs. 14a and 14b), the radar estimates of rainfall would have been significantly higher than <br /> <br /> <br />plotted as evidenced by the large area above the horizontal dashed line in Fig. 14b. For example, <br /> <br /> <br />if the rain rate threshold had been set at 144 rnm h" or 5.7 in h" (equivalent to 55 dBl), the ;/ <br /> <br /> <br />basin-maximum storm-total rainfall would have increased from 72 rnm (2.85 in) to 104 rnm <br /> <br /> <br />(4.09 in). The maximum reflectivity at any bin within the basin exceeded 51 dBl for an hour <br /> <br /> <br />and a half, from 0159 to 0327 UTC, and the largest observed hybrid scan reflectivity of 62.5 dBl <br /> <br /> <br />occurrt:d at 0217 UTC. This maximum reflectivity would correspond to an unreasonably large <br /> <br /> <br />instantaneous rain rate of 19.5 in/hr using the default l-R relationship, and it is likely a radar <br /> <br />sample volume located in a hail region. <br />Basin-maximum one-hour rainfall peaked at 0315 UTe at 62 rnm (2.44 inches), while <br /> <br />basin-averaged one-hour rainfall never exceeded 18 rnm (0.72 inches) (Fig, 14c). This large <br /> <br />discrepancy is a result of the fact that the heaviest rainfall occurred only in the lowest portion of <br /> <br />22 <br />