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10. Development of a Snow Accumulation Algorithm for the NEXRAD Radar System, First Version: June 1996 10.1 Introduction The MOD specifies several milestones for the delivery of results in the development of the Snow Accumulation Algorithm (hereafter Snow Algorithm) for the NEXRAD radar system. The following sections and appendices describe the Snow Algorithm itself and not the associated data gathering activities (secs. 2 to 6), or their results in specifying a relationship between effective reflectivity factor (Ze) and snow water equivalent (8) on the ground (sees. 7 to 9). The appendixes give specific details for the various specialists who will be involved in the further programming or use of the Snow Algorithm. · Appendix B contains appendix B of the MOD: Algorithm Documentation Requirements. It specifies a document containing nine sections: 1. Source. 2. Bibliography 3. Functional Description 4. Functional Comparison 5. Statistical Performance 6. Operational Performance 7. Adaptable Parameters 8. Strengths and Limitations 9. Future Enhancements However, this report has a different structure. The rest of appendix B identifies the sections of this report that fulfill those requirements. · Appendix C is the same as appendix C of the MOD: Criteria for Acceptance of Deliverables. It specifies numerous characteristics to be included in the Snow Algorithm.. · Appendix D summarizes the tasks specified in the SOW given in the MOD and gives the delivery timetable and preliminary results. 10.2 Relationship to Other OSF Software Programs This Snow Algorithm is partly based on procedures already in use with the NEXRAD system, specifically the PPS (precipitation processing subsystem), intended for rain, and Doppler winds (VAD) portions. Where appropriate, the same PPS or VAD subroutine names have been used where they are identical or accomplish the same thing. Likewise, a few of the variables are the same. The program structure differs in that it does not use the same shared memory as the PPS and V AD routines because of the complicated addresses in those routines and the reduced program memory space in the development versions. The enclosed simpler program structure is expected to be rewritten into the NEXRAD software style. The programs use reflectivity (Ze) data from Level II tapes consisting of dBZ, offset, multiplied by 2, and offset again to yield integer numbers called "biased dBZ" in the PPS software ranging from 0 to 255; 0 indicates that Ze is below the detection level for the WSR- 88D. Velocity data are also rescaled to a range of 0 to 255. Resulting numbers are therefore not "biased" in the normal dictionary sense but are resealed into the byte range of numbers. 37