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<br />of heavy showers moved into Fort Collins. Like the early rains, these evening showers <br />seemed to hug the base of the foothills. The rains increased in both area and intensity between <br />1800 and 1900 MDT with hourly accumulations of close to one inch in southwest Fort <br />Collins, but with lighter rains over most of the Fort Collins area from the lower foothills out <br />onto the plains. A few bolts of lightning accompanied these rains, but electrification was <br />surprisingly little considering the intensity of the rains. Unlike so many Colorado storms, no <br />hail was reported. Many individuals independently noted how warm the rain seemed. <br />Raindrop sizes were not large, considering the intensity of the rain, and no strong winds <br />accompanied the rains - at least not in the immediate Fort Collins area. One report of strong <br />winds blowing out of the north (out from the storm center) was filed by a weather watcher a <br />few miles northwest of Loveland. <br /> <br />Extreme rainfa1l rates may have begun earlier, but the first burst to reach the recording rain <br />gauge at the Atmospheric Science Department on the Foothills Campus of Colorado State <br />University (extreme west Fort Collins just east ofHorsetooth Reservoir) began shortly before <br />7:00 p.m. (1900 MDT). For a few minutes, rainfall rates approached three inches per hour <br />and then tapered off again. Surges of extremely heavy rains seemed to emanate from <br />southwest Fort Collins and spread northward in waves over the west side of the city. Heavy <br />rains also reached northern portions of Fort Collins and continued northward into the county, <br />while only light to moderate rains were observed over southeast Fort Collins. <br /> <br />Lightning activity increased around 2000 MDT as heavy rains continued to fall. What began <br />as minor street flooding became increasingly more serious over the western half of Fort <br />Collins as the downpours continued. Then for a few minutes parts of town experienced a lull <br />in rainfall intensity before 8:30 p.m. (2030 MDT). Soon after that, the rains let up or ended <br />completely just a few miles south of town, in the vicinity ofMasonville southwest of Fort <br />Collins and over southeastern portions of the city. At the same time, cloud watchers east of <br />Fort Collins noted the storm clouds that had seemingly been spreading eastward and <br />northward appeared to retreat back towards the west and condense into a small but ominous <br />cloud mass over and west of the city. <br /> <br />Most summer thunderstorms would have begun to dissipate or move away by this time, but <br />this storm was an exception. Instead of weakening, rainfall intensities increased again, and the <br />most intense rains were still ahead. From about 8:30 to 10:00 p.m. (2030 to 2200 MDT) <br />extremely heavy rain, of a magnitude rarely experienced in northern Colorado, was localized <br />over an area of a few square miles centered not far from the comer of Drake Road and <br />Overland Trail in extreme southwestern Fort Collins. Based on a variety of individual <br />observations and numerous reports of over-topped rain gauges, it appeared that rainfall totals <br />for this 90-minute period approached or exceeded five inches over the approximate area <br />delineated by Taft Hill Road on the east, the crest of the hogback formation that forms the <br />eastern edge ofHorsetooth Reservoir on the west, the western extension ofHorsetooth Road <br />on the south and approximately Elizabeth Street on the north (see Figure 13). This area <br />includes much of the Spring Creek watershed. Maximum instantaneous rainfa1l rates likely <br />exceeded 5-6 inches per hour at times. With these extreme rainfa1l rates falling on a surface <br />already covered with flowing water, incredible volumes of water accumulated that moved <br />downhill from approximately west to east across Fort Collins initiating the devastating <br /> <br />31 <br />