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I I I I I I I I I I I I I I I I I I I 1. INTRODUCTION The Bureau of Reclamation (Reclamation) was successful in proposing to accomplish certain tasks for the GEWEX Continental-Scale International Program (GCIP). GEWEX is the acronym for the Global Energy and Water Cycle 'Experiment. Reclamation is providing significant cost-sharing toward accomplishment of these tasks through its Research and Technology Transfer (RTr) Program. Consequently, the progress reported herein was jointly funded by GCIP and RTT during the past several months. In accordance with Reclamation's Proposal No. GC97-377, applied research has been pursued under two major tasks during the first year of activity, which began in April 1997. Reclamation's Statement of Work, submitted during March 1997, discussed these two tasks, which are briefly described below: a. Develop a Range Correction Scheme for Reclamation's Snow Accumulation Algorithm (SAA). A prototype SAA has been developed with support from the NEXt generation weather RADar (NEXRAD) Operational Support Facility and from Reclamation. The current version of the SAA is undergoing field tests at Albany, NY, during the 1997-98 winter. The Albany forecasters are finding SAA estimates of both snow water equivalent (SWE) and snow depth to be useful products with quite reasonable accuracy (John Quinlan, personal communication). The Albany version of the SAA uses a simple range correction scheme based on comparison of radar and snow board observations from a prior winter. Such comparisons are not practical at most radar . locations. However, Reclamation proposed development of a scheme based on radar observations alone that could be applied to any NEXRAD Weather Surveillance Radar-1988 Doppler (WSR-88D) radar site. As discussed in section 2 of this report, Reclamation is using the vertical profile of reflectivity, measured by the radar itself, to estimate corrections needed to compensate for known radar SWE underestimation with range. The first attempt discussed herein uses the seasonal average vertical profile of reflectivity. However, future work may use real-time observations of the vertical profile of reflectivity to refine mid- and far-range adjustments. Real- time adjustments are already being used in some European countries. For reference, the only operational precipitation algorithm currently being used by NEXRAD radars does not employ any range correction scheme. This Precipitation Processing Subsystem (PPS) algorithm provides reasonably accurate estimates of convective rain but seriously underestimates stratiform rain at mid to far ranges (Klazura et al. 1998).