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<br />Hourly measurements from a high resolution gage were obtained from other researchers in both the <br />Denver and Minneapolis areas. Each was sUITounded by a large Wyoming snow fence shield in an <br />otherwise exposed location. These 2 gages were not installed and operated for this project. Data from <br />these non-project gages were used because they were available from knowledgeable researchers. <br />Furthermore, some publications indicate Wyoming wind shields allow reasonably accurate gage <br />measurements to be made in windy locations. Other publications present a contrary view. These <br />differences in opinion may well be based on different standards of presumed "true snowfall" which is <br />quite difficult to establish with certainty in the generally windy areas where large Wyoming wind shields <br />are deployed. <br /> <br />The authors have no experience with Wyoming shields and no firm opinion about the accuracy of <br />resulting S accumulation measurements. However, when the data from the 2 Wyoming shield locations <br />were analyzed and compared with the values from nearby gages shown in figure 5, results were markedly <br />different. The 2 Wyoming shielded gages had smaller a values, well below their respective KFTG <br />and KMPX lines offib'1lre 5. This suggests the Wyoming shielded gages, located in windy exposed <br />locations, may have overcaught snowfall similar to the "shelterbelt effect" which results in trapping of <br />horizontally transported snow. Moreover, the values of R (correlation coefficient) between radar <br />estimates and gage observations were relatively small for these two gages, with one producing the <br />smallest R calculated of any gage or snow board in this study. In view of this evidence, it was decided to <br />use only observations from Reclamation-installed Universal gages or from the snow boards already <br />discussed in development of Ze-S relations. <br /> <br />5.4 Locations Relative to Radars <br /> <br />It is desirable to locate snow observing sites intended for Ze-S comparisons as near the radar as practical. <br />Such locations minimize the vertical distance between the radar beam and the surface, which reduces <br />uncertainties caused by wind advection of snow particles and the vertical profile of Ze' In addition, the <br />volume sampled by the radar increases with range as the beam broadens in width and height. So the <br />representativeness of a surface point observation for the overlying range bin or bins becomes increasingly <br />uncertain at more distant ranges. However, as a practical matter, these factors must be weighed against <br />usually greater ground clutter contamination near the radar and whether suitable surface observing sites <br />exist near the radar. <br /> <br />5.5 Snowfall Measurement Concerns <br /> <br />Figure 2 summarizes some of the concerns with measuring snowfall and comparing it with radar <br />observations. In addition to those mentioned above, there is a great difference in sample volume between <br />a radar bin and a gage, each for a nominal I-second sample, of about 11 orders of magnitude. Of course, <br />this vast difference is somewhat reduced because the gage continually samples falling snow particles <br />while the radar rapidly "sweeps" a given range bin at about 6 or 10-minute intervals depending upon the <br />VCP (volume coverage pattern). Natural fluctuations in either measurement can be missed by the other. <br />The tradeoffs involved in selecting a snow observing site near a radar are further addressed in the <br />discussion of site selection in the Denver area by Super and Holroyd (1996). <br /> <br />13 <br />