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<br />Probable Maximum Precipitation (PMP) Site Specific Study for Cherry Creek Reservoir <br /> <br />Reviewer Comments regarding draft of March 2003 <br /> <br />Nolan J. Doesken (completed 5,14/2003) <br /> <br />After considerable review and consideration, I wish to submit the following comments. <br /> <br />I believe the project team has done an admirable job with a frustrating, controversial, <br />open-ended project, especially considering the modest budget. The final report is <br />comprehensive and addresses, in my estimation, all the requirements set forth in the <br />initial Scope of Work. The team, with a tradition of competing for projects rather than <br />working together, overcame most differences to reach a reasonable conclusion. I accept <br />the fact there will never be a totally satisfactory clear and clean ending or a single totally <br />defendable final answer in this PMP arena. While I have some doubts and concems <br />which I will list below, I believe the authors have followed a traceable path that could be <br />duplicated, more or less, by others at a later date if necessary. Their resulting PMP <br />value(s) for Cherry Creek above Cherry Creek Reservoir, while considerably lower than <br />the value published in a previous site specific study performed by the National Weather <br />Service, do appear defensible. However, I have some concerns that I hope the study team <br />can address before a final report is submitted and policy decisions begin to be made. <br /> <br />1) I was disappointed on several occasions by drafts with incomplete text and <br />occasional missing pages. While trivial in many ways, these problems did <br />frustrate an efficient review process. <br /> <br />2) The results of sensitivity studies were helpful in subsequent interpretation of <br />procedures and results, One quickly sees the extreme sensitivity to dewpoint <br />temperatures. It does indeed seem logical to try to determine appropriate inflow <br />dewpoints as accurately as possible. Since I am a long-time weather observer <br />familiar with measurements of dewpoint temperature, the ability to measure it <br />accurately to anything better than one degree F is unlikely. Since storm <br />representative dewpoints may be based on an average of data from several times <br />and places, do the authors feel that this averaging does allow estimations to 0,5 <br />deg F instead of whole degrees? I could not justify to the nearest 0.5 deg F based <br />on actual point measurements -- averaging over several obs?? Then maybe. <br /> <br />3) The discussions of basin topography and the elevation profiles with respect to the <br />Palmer Divide are very informative, especially in combination with the analysis <br />of sub-cloud and cloud layer winds (Sec 4,2). While the big storms on our storm <br />list mostly provide low-level moisture from the southeast, I still ponder the less <br />frequent but arguably not impossible scenario oflow-level moisture coming from <br />the SE at and above the crest of the Palmer Divide, but, at the same time, also <br />converging cyclonically up the South Platte Valley into Cherry Creek from the <br />northeast and north. While the South Platte dew points may be a bit lower, we <br />