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Last modified
1/25/2010 7:10:01 PM
Creation date
10/5/2006 2:31:58 AM
Metadata
Fields
Template:
Floodplain Documents
County
Statewide
Community
State of Colorado
Stream Name
All
Basin
Statewide
Title
Colorado Extreme Storm Precipitation Data Study
Date
5/1/1997
Prepared For
State of Colorado
Prepared By
CSU
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />temperatures and humidity near the surface and the rate of cooling of the atmosphere with <br />height. The height of the bases of convective clouds can be estimated using the LCL. It is <br />interesting the cloud bases are typically highest in late June - a time when the frequency of <br />extreme precipitation events in Colorado is low. <br /> <br />For each of the storms assembled on the final list of most extreme storms affecting <br />Colorado that have occurred since 1958, soundings were extracted and examined both for <br />Grand Junction and Denver and also for upper air sounding sites in adjacent states - <br />Albuquerque, New Mexico; North Platte, Nebraska and Salt Lake City, Utah. <br /> <br />An item of particular interest in this study was determining how unusual upper <br />atmospheric conditions were during extreme precipitation events with respect to the <br />"normal" range of conditions shown in Figures 3-6. Soundings taken at Grand Junction <br />and Denver near or during the time of several of the extremely heavy storms were <br />analyzed and the results compared to the normal climatological ranges to see if those days <br />stood out as extremely unusual in terms of any of these variables. What we discovered <br />was that for nearly all of the storm events tested, sounding conditions for any single <br />variable were not extreme. Precipitable water was usually more than the 50th percentile <br />and often more than the 75th percentile but did not exceed the 95th percentile. Upper <br />level temperatures varied widely. Freezing levels also were highly variable but were <br />typically higher than the median, especially for summertime Local Convective storms. <br />Lifted Condensation Levels were usually lower than normal, but not necessarily extremely <br />low. <br /> <br />There are a number of reasons why these results are not surprising. First, the soundings <br />were usually taken some distance away (both in time and space) from the extreme storm <br />events in question. Therefore, these soundings did not truly indicate the atmospheric <br />conditions in the immediate vicinity of each heavy rain storm. Secondly, a two- <br />dimensional sounding, while informative, certainly does not describe all features of the <br />three-dimensional atmosphere in which a storm develops and exists. For example, <br />important features of surface convergence and upper air divergence will not be identifiable <br />from a single sounding. <br /> <br />The environment of the storms have two critically important characteristics. One is the <br />thermodynamic structure of the atmosphere and the second is the dynamic features of the <br />atmosphere. The upper air sounding describes primarily the thermodynamic features. The <br />dynamic features are equally important, but each individual sounding contains little <br />information to define the dynamic environment. Consequently, the soundings produce <br />useful but not definitive information about the storm environment. <br /> <br />15 <br />
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