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<br />Technical Review Panel Member Nolan J. Doesken Review Comments dated <br />May 14, 2003 <br /> <br />The A W A team acknowledges Mr. Doesken's opinion that the A W A team reached a <br />reasonable conclusion and that the resulting PMP value(s) appear defensible. <br /> <br />Comments <br />I) The A W A team apologizes for the incomplete text and missing pages in previous <br />draft reports. <br /> <br />2) The application of rounding dew point values to the nearest half-degree is used to <br />increase the analysis precision to that warranted by standard mathematical averaging procedures. <br />An example of integer values averaged to produce a value to the nearest half integer is the <br />determination of the shape ratio used in HMR 52. Section 3.2 discusses storm isohyetal shapes <br />with an integer value of the storm shape ratio determined for each of 53 major storms, i.e. 53 <br />integer values. Based on a NWS analysis of these integer shape ratios, a ratio of2.5 was adopted <br />for use. <br />The A W A team recommendation is to use the nearest half-degree when dew points values <br />from various stations are used. The recommended procedure is the use of standard mathematical <br />rounding procedures. Use ofthese standard procedures will not bias the analysis either upward <br />or downward nor will it "shave half a degree off observed values" since it rounds up as well as <br />rounding downward. It is no more bias than rounding to the nearest degree. Half degree <br />rounding should not be used with observations from a single station but should be used with dew <br />point data from multiple stations. <br /> <br />3) The scenario presented is an appropriate one. The A W A team discussed similar <br />scenarios but concluded that 1) cooler, drier air would be injected into the storm and 2) the cloud <br />steering wind would orient the rainfall isohyetal pattern across the basin. The combination of <br />these two factors would make such a storm a non-PMP and/or non-PMF event. <br /> <br />4) The A W A team evaluated two Montana storms recommended by the NWS, the 1969 <br />Spring Brook storm and the 1921 Gibson Dam storm. The Spring Brook storm is a potential <br />candidate storm but when transpositioned to the Cherry Creek basin had less rainfall than some <br />of the Colorado storms. The Gibson Dam storm occurred over and west of the first upslopes and <br />is not transpositionable to the Cherry Creek basin. HMR 55A, Figure 8.3 shows the transposition <br />limits for the Gibson Dam storm which clearly do not include the Cherry Creek basin location. <br />HMR 44 also considered this storm for transpositioning over the South Platte River basin. It was <br />transposed to the western slopes of the South Platte basin, well to the west of the Cherry Creek <br />basin. <br /> <br />5) The storm isohyetal patterns used in the transpositioning process were either digitized <br />from previous analyses or developed using ArcView GIS. The Fort Collins and Pawnee Creek <br />storms were developed using the GIS software. The isohyetal patterns these storms that were <br />produced in previous analyses can be digitized and used but neither of the storms are large <br />enough to impact the study results. The most significant storm in the study was the Penrose <br />storm, 1921. The storm isohyetal pattern was developed using GIS software. When compared to <br />