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<br />unlikely that an adequate number of real-time gage observations of S accumulation, with <br />sufficient accuracy, will be available in the foreseeable future. <br /> <br />II. By memo dated October 2, 1996, which accompanied MOU Modification No.2, increase <br />Reclamation's level of involvement in real-time testing of the SAA during the 1996-97 winter: <br />The prototype SAA was subsequently modified for real-time use. Testing was done in Cleveland <br />and Minneapolis NWS FOs using the WDSS (Warning Decision Support System) developed and <br />maintained by the NSSL. Modifications including a simple range correction scheme were added <br />for the testing at Albany during the 1997-98 winter. <br /> <br />12. Investigate means of meaningfully partitioning Ze-S data where S is the instantaneous snowfall <br />rate, and also SD data (MOU task 4.b, (3)): While the storm types differed amongst the study <br />areas, within each area the types were generally the same and therefore not appropriate for <br />partitioning. For example, virtually all snowfall episodes sampled near Denver were upslope <br />storms, and all but 3 episodes east-northeast of Cleveland were lake effect storms. <br /> <br />3. BASIC CONSIDERATIONS <br /> <br />3.1 Analysis Style <br /> <br />As discussed further in section 6, there are two basic approaches normally used in relating radar <br />measurements to precipitation, primarily proceeding from the relative mathematical simplicity of rain <br />drops. One basic approach looks at the individual precipitation particles and derives Z (radar reflectivity <br />factor) from the sum of the sixth power of their diameters. That is related to the rain rate, R, of those <br />same particles. Radar measurements are not used in this approach. For snow, the melted droplet <br />diameter is used. <br /> <br />The other basic approach examines what the radar actually measures, Ze (equivalent radar reflectivity <br />factor), often simply called "reflectivity." This radar measurement is related to bulk precipitation <br />measured at the ground. Being primarily interested in the practical applications of the resulting <br />algorithm, we have chosen the latter approach of dealing with what a radar actually measures. <br /> <br />3.2 Data Gathering <br /> <br />One of the major tasks in developing the SAA has been to determine appropriate relationships between <br />Ze and the instantaneous snowfall rate S. (S is used in this report to denote both the instantaneous rate of <br />snow water equivalent and its accumulation over hourly or longer periods.) Of great importance was the <br />accurate measurement of accumulated Sand SD at the ground, and the acquisition of calibrated, <br />uncluttered, and unmodified (by clutter suppression) measurements of Ze' Measurements of Sand Ze <br />were then related through the standard power law equation (see equation (3) in section 6) by determining <br />the coefficient and exponent values with an optimization scheme. <br /> <br />The offices maintaining individual WSR-88Ds, usually NWS FOs, were responsible for calibration of <br />their radars. The OSF coordinated with each office prior to the winter of data collection to be used for <br />this study. Each office assured the OSF that their radar was properly calibrated and the authors have <br />assumed that was the case in the absence of special calibrations. Five WSR-88Ds from different snow <br />producing regions of the nation are the focus in this report. These are KENX, 30 km SW of Albany on a <br /> <br />5 <br />