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<br />It was hoped that at least one snow measurement site could be located within 20 km of the <br />radar to provide the primary observations for calculation of a and J3 in equation (1). The area <br />within more than a 50-km radius of the Denver NEXRAD is generally wide-open prairie with <br />the metropolitan area built on the western portions. The "Denver" WSR-88D is actually <br />located at the Front Range Airport, almost 40 km east of downtown Denver. Consequently, <br />the ideal gage site of a small clearing within an extended forest does not exist near the radar. <br /> <br />Diligent searching of many stream bottoms, parks, cemeteries, military installations (Rocky <br />Mountain Arsenal, Fitzsimons Medical Center, Lowry and Buckley Air Bases) and some light <br />industrial complexes did not reveal adequately protected gage sites even within 30 km of the <br />radar. A possible exception was that some shelterbelts were found consisting of rows of <br />conifer trees partially or completely surrounding farm homes and buildings, some within 10 <br />to 15 km of the radar. However, although such sites have considerable local protection, the <br />areal extent of such protection is quite limited, rarely consisting of more than a few rows of <br />trees. These shelterbelts, surrounded by large areas of open prairie and typically located on <br />windy hilltops, likely would act as "snow traps." Shelterbelts probably catch well above <br />average snowfall during the frequent periods with snow blown across the prairie by strong <br />winds. In contrast, most blowing snow in an extended conifer forest would be trapped among <br />the numerous tree tops so that any additional catch within small clearings should be minor. <br /> <br />7 <br /> <br /> <br />After considerable examination of the land and structures within about 30 km of the Denver <br />WSR-88D, the best snow observation sites were found in some extended subdivisions of <br />homes. Some subdivisions consist of many 2-story houses with solid wood fences, typically <br />6 ft high, surrounding most back yards. Large established trees add to the general wind <br />protection. Such sites may approximate the "ideal" clearing in conifer forest site. Literature <br />evaluating the accuracy of snowfall measurement in fenced suburban yards is not known to <br />exist, although the gage site classification scheme of Sevruk and Zahlavova (1994) considers <br />just the vertical angle to the tops of obstacles, whether Structures or trees. They found that <br />sites surrounded by obstacles 20 to 250 above the horizon provided good protection. <br /> <br />Experience with suburban sites within 50 km of the Denver NEXRAD was encouraging <br />during the 1995-96 winter. Hourly snowboard and wind observations were made at three <br />carefully chosen sites in established neighborhoods. At each location, the large majority of <br />hours with snowfall had winds less than 1 m S.l at gage orifice level (-1 m a.g.!.). <br /> <br />Another major consideration in choosing snowfall observing sites is the presence or absenee <br />of ground clutter. This factor is especially important with the WSR-88D radar in its present <br />configuration because no automatic record is made of the ground clutter suppression scheme <br />in use at any time. Ground-clutter suppression is applied at the RDA (radar data <br />acquisition) unit prior to data stream transmission to the RPG (radar product generator). <br />Further description of the WSR-88D system and an overview of available analysis products <br />is given by the Federal Meteorological Handbook No. 11 (1991) and Klazura and Imy (1993). <br /> <br />The ground clutter suppression scheme, described by Chrisman et al. (1994), can use a clutter <br />bypass map, notch width map and operator-defined clutter suppression regions in various <br />combinations to suppress returns in regions with potential or actual ground clutter. The <br />particular clutter suppression scheme in use can affect both the resulting Z. and Doppler <br />velocity fields in unknown ways. MOUs were established between the OSF and the Albany, <br />Cleveland, and Denver WFOs which provided, among other things, record-keeping of the <br />suppression scheme in use. Howevet, it was still judged best to avoid cluttered regions for <br />