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<br />OOJ395 <br /> <br />\ <br /> <br />3. In 1981 more than half (57 percent) of all flash flood <br />warnin9s had no lead time. Another 20 percent of the <br />warnings had from a few minutes to an hour for the <br />public to prepare. <br /> <br />4. Average lead time for the flash flood warnings was 30 <br />minutes and, if only warnings with a positive lead <br />time are counted, then in only 35 percent of all flash <br />floods is the public warned in time to take some action. <br /> <br />These statistics and recent updates are hardly encouraging and may have <br />led to an unconscious effort by th~ hydrological community to engineer <br />the "meteorology" out of the flash flood prediction problem, Many <br />current programs place a reliance on the remote sensing of rainfall and <br />runoff coupled with computerized basin response models to trigger the <br />flash flood warning messages needed for the public to respond. Such <br />attempts may be doomed to failure because the event happens too quickly <br />to rely on a "measured-computed" warning response. What is needed is <br />a true hydro-meteorological systems approach that produces reliable, <br />accurate forecasts of rainfall and potential floodin9 before the first <br />drop of rain has formed! Such a model program has been serving the <br />Denver metropolitan area through Urban Drainage & Flood Control District <br />(UDFCD) since 1979 with reliable results. The program embodies a <br />symbiosis of hydrology and meteorology. <br /> <br />UDFCD Flash Flood Prediction Program (F2-P2) <br /> <br />The Urban Drainage & Flood Control District of Denver (UDFCD) has <br />sponsored a flash flood prediction program (F2-P2) serving the six <br />county Denver, Colorado metropolitan area since 1979. Impetus to secure <br />program funding was derived from the disasterous 1965 Cherry Creek <br />flooding of Denver and the deadly 1976 Big Thompson Flash Flood. The <br />F2-P2 is largely the result of joint interaction between the engineers <br />and hydrologists of UDFCD and the meteorOlogists of Henz Kelly & Associates <br />(1983-1985) and the now-closed GRD Weather Center, Inc. (1979-1982). <br />Unlike many local flash flood programs that rely solely on ground-based <br />remote rain sensing and/or National Weather Service forecasts the Denver <br />F2-P2 depends heavily on predictions made by private sector meteorologists <br />which are issued to local government focal points. While the F2-P2 <br />cooperates with the National Weather Service the F2-P2 forecasts are made <br />independently by the private meteorologists. <br /> <br />The groundwork for the F2-P2 relies on the sound hydrologic <br />background that has been given to the private meteorologists by UDFCD <br />engineers for each of the flash flood prone basins and urban areas in <br />the District. This knowledge represents a qualitative contribution that <br />has proven very valuable. If this knowledge is the groundwork then the <br />clutch that makes the program work is the meteorologists' contributions <br />"when it matters, before the fact". It is the sound physical assessment <br />of the rainfall production capability of the atmosphere as it conforms <br />to local topographic and mesometeorol09ical influences interpreted in <br />light of their hydrological consequences. <br /> <br />-2- <br />