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Last modified
1/25/2010 6:44:42 PM
Creation date
10/5/2006 12:11:28 AM
Metadata
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Floodplain Documents
County
Statewide
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State of Colorado
Stream Name
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Basin
Statewide
Title
Extreme Precipitation Study: Storm Data and Interpretation from HMS Storm Files
Date
4/1/1997
Prepared For
State Climatologist
Prepared By
Henz Meteorological Services
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />~. <br /> <br />. ,",~, . -_"_,. '_,_......~c_-,.."-"_.o:,,.,,'_ <br /> <br />was reported on either day. The close proximity of both these events in space and <br />time provides a strong motivation to include both train echo rainfall and consecutive <br />periods of thunderstorm rainfall to the General Convl:ctive Storm PMP scenario. <br /> <br />3.4 Big Thompson Canyon, Colorado; July 31, 1976 <br /> <br />This historic event is considered a General Convective StOlID and is well documented in <br />the literature. An early general overview of the flooding in the Big Thompson Canyon is <br />given in Storm Data as follows: <br /> <br />"Thunderstorms caused a major flash flood in the Big Thompson River Canyon. <br />Path of destruction began near Estes Park and extended for 25 miles to Loveland. <br />Survivors told of a wall of water 6 to 8 feet high in the narrow canyon ofth,e Big <br />Thompson and its north fork, where hundreds of cars and campers wen~ strewn. <br />Much of Highway 34 was washed away between Estes Park and Loveland. On <br />Sunday, August 1, 840 persons were evacuated by helicopter with 250 repoJrted <br />injured. One of the hardest hit towns was Glen Haven about 6 miles northeast of <br />Estes Park. About 200 persons were still stl'anded in the canyon at 6 p.m. Sunday <br />with 56 known dead. On Monday August 2 President Ford declared Larimer <br />County a major disaster area. By September 1, 131 bodies had been recovered and <br />123 identified. Expected death toll 156. The river was 20 feet in places over its <br />normal 4-5 foot depth. Estimated property damage was 29 million dollars. Heaviest <br />rain was in an oval shaped area 3 miles along the river and 1 mile wide with the west <br />edge of the oval just east of Glen Comfort. 9.9 to 11.9 inches of rain fell in the <br />area." <br /> <br />McCain et al (1978) provide the following later summary information about this event <br />and the Poudre River and Rist Canyon event (see Section 3.5 of the present report): <br /> <br />"Devastating flash floods swept through the canyon section of Larimer County in <br />north-central Colorado during the night ofJ uly 31-August I, 1976 causing 139 <br />deaths, 5 missing persons, and more than $35 million in total damages. The brunt <br />of the storms OCCUlTed over the Big Thompson River basin between Drake and <br />Estes Park with rainfall amounts as much as 12 inches being reported during the <br />stonn period. In the Cache la Poudre River basin ::0 the north, a rainfall amount <br />of 10 inches was reported for one locality while 6 inches fell over a widespread <br />area near the central part of the basin. <br /> <br />"The storms developed when strong low-level easterly winds to the rear of a polar <br />front pushed a moist, conditionally unstable ainnass upslope into the Front Range <br />of the Rocky Mountains. Orographic uplift released the convective instability, <br />and light south southwesterly winds at middle and upper levels allowed the storm <br />complex to remain nearly stationary over the foothills for several hours. <br />Minimum entrainment of relatively moist air at middle and upper levels, very low <br /> <br />13 <br />
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