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<br />OOJ337 <br /> <br />TABLE 1 <br /> <br />VERIFICATION OF SEASON-BY-SEASON ECR DAY FORECASTS (1979-1985) <br />FOR DENVER, COLORADO FLASH FLOOD PREDICTION PROGRAM <br /> <br /> Forecasts of <br />Length ECR Days False Alarm Proba b il i ty <br />of Season(Day) Year Hits Misses Accuracy Rate of Detection <br />154* 1979 17(30) 9(2) 94% 35% 85 <br />154* 1980 23 12 93% 34% 100 <br />154 1981 31 9 94% 23% 100 <br />154 1982 34 8 95% 19% 100 <br />154 1983 32 5 97% 14% 100 <br />154 1984 32 6 96% 16% 100 <br />154 1985 25 3 98% 11% 100 <br />1,078 194 52 95% 21% 98% <br />*Sta tis tics verified by 1981-1985 standards <br /> <br />Certainly a comparison of the NWS flash flood watch and warning <br />statistics in the introduction and the Denver F2-P2 suggests something <br />is being done very correctly in the Denver F2-P2, The difference is in <br />the physical assessments made of the pre-storm environment to accurately <br />assess the rainfall production potential of individual thunderstorm <br />systems and the subsequent updating of these early predictions made just <br />prior to the beginning of the storm and during its duration. <br /> <br />HKA's Flash Flood Prediction Program (F2-P2) Concept <br /> <br />HKA has conducted a flash flood prediction program (F2-P2) for <br />the six county Denver metropolitan area since 1979 for the Urban <br />Drainage & Flood Control District (UDFCD), The Denver F2-P2 provides <br />flash flood and urban flooding predictions for an area roughly 60 by <br />30 miles. The area is comprised of rolling prairie on the east, a <br />densely populated and urbanized central core and rugged foothills <br />regions on the west and south (Figure 2). Additionally river and stream <br />basins are routinely metwatched for flooding potential in mountain basin <br />areas which cover a region to the west and south over four times as large <br />as the UDFCD. <br /> <br />The successful prediction of flash floods and urban flooding in <br />the F2-P2 depends on the successful integration and interpretation of <br />a variety of data sources by highly trained meso-meteorologists. The <br />data sources relied on include: <br /> <br />a. Standard synoptic surface and upper air observations <br />b. Half-hourly satellite photos <br />c. Continuous 10 cm radar observations <br />d. Surface mesonet observations <br />e. Rainfall measurements from canyon gage networks and observers <br /> <br />-4- <br />