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<br />high for this part of the country. Around 6:00 PM MDT, bands of heavy showers began <br />again (Figure 4). Once more, the heaviest showers were concentrated near the foothills, <br />A few rumbles of thunder accompanied the rain, but lightning activity was not <br />remarkable. As the evening progressed, rains increased. Winds were surprisingly light, <br />and temperatures remained very mild. Many residents noted the unusually wann rain and <br />the lack of any hail. Around 8:30 PM, after more than two hours of heavy rain, the rains <br />diminished east and southeast of the city. At this same time, the storm's intensity <br />increased in western portions of Fort Collins, From 8:30 to 10:00 PM, the heaviest <br />sustained rainfall in memory, with rainfall rates occasionally reaching six inches per hour <br />over southwest Fort Collins, inundated the city and sent huge volumes of runoff flowing <br />downhill across the city from west to east. After this awesome crescendo of rainfall, the <br />rains ended mercifully and abruptly between 10:00 and 10:30 PM in southwest Fort <br />Collins with lighter rains continuing north of town until after 11 :00 PM. When the <br />evening storm was over, more than 10 inches of rain had fallen in the Spring Creek basin <br />in southwest Fort Collins (Figure 5) with five to eight inch totals widespread over the <br />western half of the city. Remarkable rainfall gradients were noted southeast of the storm <br />center with less than two inches of rainfall over most of southeast Fort Collins. In fact, <br />many ofthe citizens were unaware of the raging flood waters heading eastward. <br /> <br />Figures 4, 5, 6, 7 <br /> <br />The official Fort Collins weather station is on the Colorado State University main campus <br />and has been measuring precipitation daily since 1889. It received very heavy rains from <br />this storm system but was approximately 3 miles northeast of the center of heaviest <br />precipitation, As measured on campus, the 1997 storm dropped 6.35 inches of rain in <br />approximately 30 hours. While not unique in terms oftotal rainfall at that location, only <br />two other storms in history have produced comparable rainfall. Analysis of hourly <br />rainfall totals show the 1997 storm to be even more remarkable. Since hourly data were <br />first published in 1940, there have been several storms with large one-hour rainfall totals <br />in excess of two inches. However, most intense storms in this area have relatively short <br />lives, and no six hour period has ever come close to dropping so much rainfall on campus <br />as the 5.3 inches that fell from 6:00 PM to 10:30 PM July 28,1997, <br /> <br />Figure 8, Table 1 <br /> <br />Meteorological radar, a remote sensing tool for precipitation detection, offered another <br />perspective on this storm. Three radar observed this storm. National Weather Service <br />WSR-88D weather surveillance radar from Cheyenne, Wyoming and Denver, Colorado <br />monitored the storm. The Colorado State University CHILL research radar, managed by <br />the Departments of Atmospheric Science and Electrical Engineering, and located north of <br />Greeley was closest to the storm. Data from the CHILL radar were used together with <br />gauge measurements to help formulate rainfall estimates in the areas immediately west of <br />Fort Collins where precipitation reports were few. <br /> <br />From an operation forecaster's perspective, the Fort Collins storm was neither eye- <br />catching nor spectacular. Based on satellite and radar signatures, several storms July 28 <br /> <br />4 <br />