SNOW ACCUMULATION ALGORITHM FOR THE WSR-88D RADAR, VERSION 1 June 1996 U.S. DEPARTMENT OF THE INTERIOR Bureau of Reclamation Technical Service Center Water Resources Services River Systems and Meteorology Group Fonn Approved OMB No 0704-0188 I REPORT DOCUMENTATION PAGE I 1 Pubhc reporting burden for this collection of mfonatlon 1s estimated to average 1 hour per response, ~ncludlngthe tlme for revlewmg lnstrunlons. searching exlstlng data sources, gather~ngand malntalnlng the data needed, and completing and revlewlng the collection of lntormat~on Send comments regardmg th~sburden estlmate or any other aspect of th~scoltectlon of ~nformat~on. lnclud~ngsuggestions for reducmg thls burden to Washmgton Headquaners Se~lces.D~rectorate for Informatton Operat~onsand Reports 1215 Jefferson Dav~sH~ghway. Sult 1204. Arlmgton VA 22202-4302. and to the OWlce of Management and Budget, Paperwork Reduction Report (0704-0188). Wash~ngtonDC 20503 1. AGENCY USE ONLY (Leave Blank) 1 2. REPORT DATE 1 3. REPORT TYPE AND DATES COVERED I ~une1996 I Final 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS Snow Accumulation Algorithm for the WSR-88D Radar, Version 1 PR 6. AUTHOR(S) Arlin B. Super and Edmond W. Holroyd, 111 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION Bureau of Reclamation REPORT NUMBER Technical Service Center Denver CO 80225 9. SPONSORIN~ONITORINGAGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORlNGlMONlTORlNG Bureau of Reclamation AGENCY REPORT NUMBER Denver Federal Center DIBR PO Box 25007 Denver CO 80225-0007 11. SUPPLEMENTARY NOTES Hard copy available at the Technical Service Center, Denver, Colorado 128. DlSTRlBUTIONlAVAllABlLlTY STATEMENT 12b. DISTRIBUTION CODE Available from the National Technical Information Service, Operations Division, 5285 Port Royal Road, Springfield, Virginia 22161 13. ABSTRACT (Maximum 200 words) This annual Bureau of Reclamation report describes the initial year of a 3-year effort to develop a Snow Accumulation Algorithm for the new network of WSR-88D (NEXRAD) radars. Snowfall measurements were made during the 1995-96 winterlspring within range of WSR-88Ds at Albany, NY, Cleveland, OH, and Denver, CO. Observations of S (snow water equivalent) from the latter two locations were related to 2, (effective reflectivity factor) measurements to determine "best fit" a and f! coefficients for the commonly-used equation 2, = dP.Recommended CY and f! values are 318 and 1.5 for Cleveland and 155 and 1.6 for Denver. Observations near Lake Erie revealed a significant range effect. The Cleveland radar underestimated snowfall beyond about 60 km. Radar-estimated snowfall amounts were about 85,61,31, and 22 percent of gage observations at 61,87,115, and 146 km,respectively. A scheme should be developed to use the vertical profile of 2, to adjust for mid- and far-range snowfall underestimates by WSR-88Ds. Initial Snow Accumulation Algorithm code is described and presented. The code development borrows from the current NEXRAD rainfall algorithm but makes several important modifications, including an advection scheme, because snowflakes can be transported tens of kilometers from the lowest tilt radar beam to the ground. 14. SUBJECT TERMS- -radar/ NEXRADI WSR-88Dl snow/ snowfall1precipitation 15. NUMBER OF PAGES 1 133 16. PRICE CODE I 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURIN CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT I I I ISN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Pmsfbed by ANSI Std. 23918 296102 SNOW ACCUMULATION ALGORITHM FOR THE WSR-88D RADAR, VERSION 1 Arlin B. Super and Edmond W. Holtoyd, Ill River Systems and Meteorology Group Water Resources Services Technical Service Center Denver, Colorado June 1996 UNITED STATES DEPARTMENT OF THE INTERIOR * BUREAU OF RECLAMATION ACKNOWLEDGMENTS It is no surprise that the efforts of many individuals were required in various aspects of special data collection or analyses which culminated in this report. Jerry Klazura provided outstanding MOU monitoring, often suggesting sources for technical information and assistance. Other NEXRAD Operational Support Facility personnel who were helpful in particular aspects of the research include Joe Chrisman, Tim O'Bannon, Bill Urell, and Colonels Tim Crum and Andy White. Several National Weather Service personnel from the Albany, NY, Cleveland, OH, and Denver, CO, WFOs made special efforts on behalf of collecting quality observations. Notable among these are John Quinlan (Albany), Bob LaPlante and Frank Kieltyka (Cleveland), and David Imy and Mike Holzinger (Denver). The three WFO MIC's deserve special thanks for allowing their staffs to assist in the snow algorithm efforts. John Kobar and Neal Lott of the National Climatic Data Center promptly furnished the many Level II data tapes that were requested for snow algorithm development. The people who were interested enough in this project to collect special snowfall observations all deserve acknowledgement. Those from the Albany area are too numerous to mention because about 90 volunteer observers were involved, but their efforts are certainly appreciated. Cleveland area observers, all of whom did a first-rate job, are Mike Bezoski, Doug Brady, David Henderson, Anthony Marshall, and Paul Mechling. The two Denver observers who deserve special mention for providing high quality hourly observations in addition to operating Belfort gages are Malcolm Bedell and Richard Kissinger. Steve Becker and Marc Jones provided quality gage measurements west of Denver. Special appreciation is expressed to Dr. James Heimbach of the University of North Carolina at Asheville. Besides providing significant counsel and being the main source of rawinsonde data throughout the field season, Dr. Heimbach found time in his busy schedule to program and rigorously test the optimization scheme used to determine radar equation coefficients, all without any monetary compensation. His considerable and generous help is very much appreciated and will not be forgotten. Dr. Paul Smith of the South Dakota School of Mines and Technology provided significant expert technical advice to Reclamation scientists. Dr. Smith carefully read the first draft of this report and made many helpful comments that improved it. Jack McPartland of Reclamation was deeply involved in all aspects of site selection, gage calibration and installation, and observer training. Curt Hartzell of Reclamation coordinated the collection of data needed for future storm partitioning. Ra Aman developed much of the programming for dealing with Level II data on a Sun workstation. Besides writing several programs used in data handling, Anne Reynolds carefully reduced most of the numerous Belfort gage charts and then double-checked them all, an exceptionally tedious job requiring extraor4inary care and patience. Special thanks are due Dave Matthews and Jim Pierce of Reclamation for providing additional resources and a flexible environment for accomplishment of this work. This work was primarily supported by the WSR-88D Operational Support Facility and the Next Generation Weather Radar (NEXRAD) Program, with additional support by Reclamation's Technical Service Center. 11 u.s. Department of the Interior Mission Statement ABthe Nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally-owned public lands and natural resources. This includes fostering sound use of our land and water resources; protecting our fish, wildlife, and biological diversity; preserving the environmental and cultural values of our national parks and historical places; and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to ensure that their development is in the best interests of all our people by encouraging stewardship and citizen participation in their care. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration. The information contained in this report regarding commercial products or firms may not be used for advertising or promotional purposes and is not to be construed as an endorsement of any product or firm by the Bureau of Reclamation. iii CONTENTS 1. Introduction. 1 2. Observations from the 1994-95 winter. 2 3. Observations from the 1995-96 winter. .. 3 3.1 Snowfall measurement considerations. 3 3.2. Albany, New York, observations. 4 3.3. Denver, Colorado, observations. 6 3.4. Cleveland, Ohio, observations. 11 4. Data processing. 13 4.1 Belfort gage chart reduction. 13 4.2 Processing of Level II radar tapes. 14 5. Comparison of Cleveland and Denver snowfalls. 15 6. Calculation of radar-estimated snowfall accumulations. 17 7. Z-S and Z.-S relationships for snowfall. 18 7.1 Introduction.. 18 7.2 Review of some Z-S relationships. 20 8. Optimization scheme for determination of a and ~coefficients. 24 9. Application of optimization scheme to Cleveland and Denver data. 25 9.1 Cleveland observations. 25 9.2 Denver observations. 32 9.3 Significance of different Z.-S relations for Cleveland and Denver. 35 10. Development of a snow accumulation algorithm for the NEXRAD radar system, first version: June 1996 . .. 37 10.1 Introduction.. .. .. 37 10.2 Relationship to other OSF software programs. .. .. 37 10.2.1 The PPS algorithm. 38 10.2.2 The VAD algorithm. .. 39 11. Functional description of the Snow Algorithm. 40 11.1 General functions and subroutines. 41 11.2 Program