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Last modified
1/25/2010 6:27:28 PM
Creation date
10/4/2006 11:48:58 PM
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Floodplain Documents
County
Statewide
Basin
Statewide
Title
Sensitivity of WSR-88D Rainfall Estimates to the Rain Rate Threshold and Rain Gauge Adjustment: A Flash Flood Case Study
Date
6/8/1998
Prepared By
NOAA
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />parameter MXPRA) of 74, 7 mm h.l, which corresponds to 51 dBl assuming the l-R equation <br /> <br />above. Any rain rates that exceed this value are capped at this value to prevent hail <br /> <br />contamination. The gauge accumulation time was set to H+OO minutes (i.e., hourly radar and <br /> <br />gauge accumulations ending at the top of every hour are used in the Adjustment algorithm), and <br /> <br />the time each hour when the bias estimation was performed was H+50 minutes based on hourly <br /> <br />accumulation data ending at 1hOO minutes. Biscan maximization was disabled by setting the <br /> <br />adaptable parameter specifYing the minimum range ofbiscan maximization to 230 km. <br /> <br />Fig. Sa shows the total reflectivity echo area time series over the 230 km range domain of <br /> <br />FTG computed from the hybrid scan of reflectivity. The period of Archive II data exanlined <br /> <br />covered the entire life cycle of the larger scale rainfall event over Colorado from formaltion to <br /> <br />dissipation. The flood-producing storm passed over the Buffalo Creek basin during the period <br /> <br />0200 to 0300 UTC (2600 to 2700 UTC in Fig. 5), shortly after the time of most widespread <br />rainfall coverage. <br /> <br />The percent areal reduction of reflectivity echoes in going from the first to the s.:cond <br /> <br />elevation angle (Fig.5b) is uSled by the PPS Tilt Test to determine if anomalous propagation <br /> <br />(AP) echoes exist. Since the reduction percentage is low throughout all but the first hour or so, <br /> <br />AP is not a problem in this case, and deep convection predominates. The time series of mean <br /> <br />reflectivity over the entire radar domain (weighted by area of the polar bins) conditionall on the <br /> <br /> <br />existence of reflectivity exceeding 7 dBl (Fig. 5c) increases to a maximum value near 24 dBZ <br /> <br /> <br />several hours into the rainfall 'event, remains there for several hours, and then decreases as the <br /> <br /> <br />storm system dissipates. <br /> <br />The Conditional Biscan Ratio (CBR) in Fig. 5d reveals how the biscan maximization <br /> <br />8 <br />
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