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<br />A variety of sources were used in determining the comprehensive Colorado storm list. <br />The data described in section 1 above was a key starting point. Other important sources <br />included Storm Data (a monthly government publication) reports, Colorado Climate <br />Center records, special engineering and consulting meteorologist's studies, Colorado <br />Department of Natural Resources Division of Water Resources flood reports, U.S. <br />Geological Survey documents and reports including Water-Supply Paper 997, Floods in <br />Colorado, by Robert Follansbee and Leon R Sawyer, local site-specific Probable <br />Maximum Precipitation consulting reports, and the formal federal Hydrometeorological <br />Reports Technical Paper Report Series and Storm Rainfall in the United States. Special <br />storm files maintained at the Denver Federal Center by the U.S. Bureau of Reclamation, <br />Flood Hydrology Group were also utilized extensively. Local sources such as historical <br />profiles and newspaper accounts were investigated to some extent, but this proved too <br />time consuming. <br /> <br />A simple definition of Extreme Precipitation was needed in order to easily and quickly <br />determine which storms qualified for consideration. Arbitrarily, it was determined that any <br />storm that exceeded the 100-year storm precipitation amounts for the specified storm <br />duration as published in the NOAA (National Oceanic and Atmospheric Administration) <br />Atlas 2, Precipitation-Frequency Atlas of the Western United States, Volume ill- <br />Colorado (1973) qualified for consideration. Also, storms that did not exceed published <br />100-year storm amounts but which were extraordinary in other ways - large in area, long <br />in duration or some combination of both - also could be considered. <br /> <br />Storms that did not exceed NOAA Atlas 2, 100-year values were still included if they <br />were already included on existing extreme precipitation lists such as those included in <br />Federal Hydrometeorological Reports for this region. <br /> <br />Each storm was given a brief descriptive name, usually based on the town, river or other <br />landmark nearest the center of heaviest precipitation. A state name was assigned to each <br />storm based on the state in which the heaviest precipitation fell. (Note: with large general <br />storms, several states may receive heavy precipitation at the same time.) The date listed <br />for each storm was the date on which the heaviest precipitation fell or the period of <br />consecutive days when a larger storm system or episode first began and finally ended. <br />Each storm was assigned one or more geographical regions based on a simple 6-region <br />system as shown on Figure 2. Storms were categorized using a highly simplified <br />meteorological typing scheme: 1) General (G) storms which were large multi-state storm <br />systems accompanied by a clearly defined low pressure system and/or frontal boundaries, <br />2) Local Convective (LC) storms which were localized thunderstorms or thunderstorm <br />complexes not clearly associated with large-scale atmospheric lifting mechanisms, and 3) <br />Local Convective Storms embedded within General storm systems (GLC). Storms with <br />air masses of tropical origin were not treated or categorized separately. A single latitude <br />and longitude was assigned to most storms based on an estimate of the coordinates where <br />the heaviest precipitation fell. <br /> <br />6 <br />