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gradually increase into the foothills of the Rocky Mountains. The region between about 12 to 50 kIn from the radar for the 300 segment noted would be expected to be clutter free. However, the bypass map shows considerable clutter in that area, perhaps caused by edge diffraction over the intervening ridge. The Denver clutter bypass map was compared with predictions from two computer programs. The OSF provided a software package (RDRHGT.FOR) written by an NWS meteorologist. The software package provides a visual presentation on a personal computer monitor of terrain underlying the radar beam for :any selected 10 of azimuth. Both beam tilt and refraction can be varied. A Reclamation meteorologist wrote separate software to plot a PPI (plan-position indicator) format map of where clutter should exist under standard refraction, and this map is in very good agreement with RDRHGT indications. Both software packages use USGS (U.S. Geological Survey) elevation files to compute where the radar beam should be relative to the underlying terrain. The October 1995 Denver clutter bypass map showed significantly more extensive clutter than predicted by the computer programs,> and a bypass map generated in April 1995 showed even more clutter. The presence of tall! buildings and towers in the Denver area could explain some but not all of the observed clutter. The clutter bypass maps may be more sensitive to clutter returns than necessary for effective clutter suppression. The clutter bypass map makes no distinction between very weak and very strong ground returns, and each pixel (somewhat larger than a l-km by 10 range bin) is only designated as either cluttered or not. Mter consideration of the disagreement between physical reasoning and the bypass map results, the snow measurement sites Wl~re located nearest the Denver radar where the RDRHGT program suggested lack of ground clutter. Even then, the nearest sites had to be established about 25 kIn from the radar, farther than desired, because protected snow measurement locations could not be found closer to the radar. As an additional approach, an operator-selected "box" was designated over one of the two measurement sites nearest the radar. Zero suppression was applied in the boxed area over gage No.2, between 18 to 30 kIn in range and 248 to 2780 in azimuth, from February 22 until the end of April 1996 when observations were terminated. This zero suppression box was used in both precipitation and clear air scanning modes. Future careful examination of bin-by-bin returns within this box should reveal whether ground clutter was present or not during snowfalls. If present, it is expected that particular range bins can be selected which avoid contaminated areas and, thereby, provide only meteorological retu:ms from snowfall. Besides use of the operator-designated box over gage No.2, the standard mode of clutter suppression with the Denver WSR-88D during the past winter was to use the clutter bypass map and moderate suppression during p,eriods when the radar was in precipitation mode scanning. In addition, two other operator-designated boxes were routinely used in more cluttered areas, neither of which affected the gages of table 3. These boxes were located from 270 to 3300 and 60 to 180 kIn, where maximum suppression applied; and from 330 to 0600 and 60 to 180 kIn, where moderate suppression was applied. When in clear air mode scanning, the entire area of Denver radar coverage was designated an operator-selected "box," and maximum suppression was applied everywhere because of frequent ground-based inversions and superrefraction (personal communication with Mike Holzinger, Denver radar focal point). 9