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Executive Summary Modernization and associated restructuring of the National Weather Service (NWS) will usher in a new era for severe weather and flood warning and forecast services in the United States. Important advances in the science of meteorology, coupled with major new technological capabilities for observing and analyzing the atmosphere, will provide unprecedented weather service improvements over the next decade. The existing systems for making weather observations and processing and communicating data and information about the weather are obsolete and costly to maintain. The modernized NWS will obtain substantially more weather data through the use of new technology that will include automated surface observations, Doppler radars, satellites, and data assimilation on supercomputers. Advanced information processing technology will be used to integrate the various data fields and to provide them to the forecaster in useful forms. This technology will also assist in the generation and issuance of improved forecasts, warnings, and other products and services. The NWS' parent agency, the Department of Commerce, in response to a request from the Chairman of the Committee on Science, Space and Technology of the U.S. House of Representatives, asked the National Research Council's National Weather Service Modernization Committee (NWSMC) to "assess the adequacy of Next Generation Weather Radar (NEXRAD) coverage for the nation..." to ensure that there will be no degradation of weather services as a result of this aspect of the moderniza- tion. Based on an intensive 6-month study, the NEXRAD Pane! of the NWSMC arrived at a strong overall conclusion that weather services on a national basis will be improved substantially under the currently planned NEXRAD network. This improvement derives from factors described in He following paragraphs. First, in comparison with the old network, the NEXRAD network will cover a much broader area of the contiguous United States. For the detection of specific weather phenomena supercelis, mini-supercelis, macrobursts, lake-effect snow, and stratiform snow the NEXRAD coverage is much greater than it was for the old system; for hurricanes, the NEXRAD coverage is complete over the entire area of risk. Second, because the NEXRAD radars meet or exceed their technical design specifications relevant to the detection of weather phenomena and because they are substantially superior to the radars they replace (even in the non-Doppler mode), the pane! concludes there is no degradation of service when a NEXRAD is located at or near the site of one of the old radars. In fact, service at those locations, which constitute the majority of sites, will be markedly improved. The pane! is confident that the introduction of NEXRADs will significantly improve overall storm detection and warning performance. Third, the NEXRAD's Doppler feature and other technical characteristics allow for greatly increased capability for short-term forecasting ("nowcasting") of thunderstorm initiation; detection of damaging winds, such as macrobursts and wind shear; and mesocyclone detection, which is often associated with tornadoes and over severe storm hazards.

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2 Assessment of NEXRAD Coverage Fourth, digital signal and data processing will permit the production and display of a wide variety of automated weather products which, in turn, will improve the forecaster's ability to rapidly assimilate and use the available data, not only from their NEXRAD but also from neighboring NEXRAD sites. Finally, the NEXRAD is only one element (although an important one) of a composite system that consists of several powerful new observational systems, including geostationary and polar satel- lites, automated surface observing equipment, lightning detection networks, wind profilers, and other atmospheric sounders. The composite system also includes cooperative networks of human observers and spotters, the skills of experienced forecasters, and improved numerical forecast models. These diverse data sets will be assimilated and integrated by an Advanced Weather Interactive Processing System at each Weather Forecast Office (WFO) that will connect the many parts of the system to permit effective use by specially trained staffs who prepare forecasts, warnings, and other products and services. NWS storm warning statistics accumulated over 5 or more years at six NWS radar sites show a distinct improvement in performance associated with the installation of a NEXRAD. Data concerning warning performance as a function of range from a NEXRAD present a mixed and somewhat confusing picture. In the panel's judgment, definitive conclusions cannot be drawn from the data available at this time. Further testing in the Modernization and Associated Restructuring Demonstration and at diverse _ . . - . ~ . . - . . ~ ~ , . . ,, , . aeoaranulc locations. with particular attention to tne verlrlcauon Gala, wll1 oe necessary lo uraw ~ ^^ . ~ ~ ~ . ~ . ~ ~ . 1 ~ , _ ~ _ ~ specific conclusions with respect to the enect or distance from tne radar on me quality or warning performance. In areas where the pre-NEXRAD radar is not replaced, and service is to be provided by a NEXRAD located some distance away, the panel's analyses show that there is a potential for some degradation in radar-detection coverage capability.] Areas of concern are illustrated in this report by a series of maps. These areas include those now covered by pre-NEXRAD radars located in northern Alabama, northern Indiana, northwestern North Dakota, northwestern Pennsylvania, and southeastern Tennessee.2 The northern Alabama area is a special case because the existing radar, which is to be decommissioned, is a functioning Doppler radar. As a result, the potential degradation in detection capability for this area is greater than for other sites in the pre-NEXRAD radar network. Also shown are a few areas where the switch from the pre-NEXRAD network to the new network results in a "degradation of service," as defined in P.~. 102-567, Sec. 702~4), due to "a reduction in existing weather radar coverage at an elevation of 10,000 ft." Degradation of ra~lar-detection coverage does not necessarily imply degradation of weather service in the forecasting and w. arnina functions. Integration of all data sources and other elements of ~ ~ V ~ . .,, . ~ . 1 1 the composite system plays a significant role in tile provision of services, permitting conslaeraole compensation for lesser detection capabilities over specific areas. However, in general, the greater the distance the pre-NEXRAD radar site is from a NEXRAD, the more likely is the degradation in radar- detection coverage in portions of the area covered by the existing radar. Similarly, there is an increased potential for degradation of associated warning services that must be compensated for by other improvements in the system through the modernization. 1 Radar-detection coverage is the area over which detectable signals are returned from various weather phenomena as the radar scans at and above the horizon. See Appendix A, page 68 for more details. 2 A site-by-site evaluation was excluded from the panel's task, but the data, criteria, and procedures to conduct such evaluations are provided in this report.

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Executive Summary 3 The panel's conclusions regarding the adequacy of coverage and service with the NEXRAD network are based on the assumption that 15 of the NEXRAD radars (listed on p. 32) currently planned to be under the control of the Department of Defense (DoD) will be operated and maintained to the standards set for the national NEXRAD network. Removal of any of these radars from the network or operation of any of them with standards and availability that are less than those of NWS-operated units will degrade radar-detection coverage. In the national NEXRAD network, there will be four NEXRADs without a nearby WFO (i.e., Yuma, Arizona; Key West, Florida; Caribou, Maine; and Cedar City, Utah). When a WFO is remote from a NEXRAD, the reliability of the NEXRAD, the dependability of services derived from it, supporting communications and back-up capability, forecast office staffing, and warning and forecast dissemination become even more-important factors in meeting the requirements of distant service areas. Based on its analyses and on the conclusions derived from them, the pane} recommends the following: 1. Where the pane} has identified specific geographic areas where degradation of radar- detection coverage may occur, the National Weather Service should examine each potentially vulnerable area to determine whether such degradation would result in degradation of associated weather services. 2. The procedures and criteria for decommissioning old radars are specified in existing National Weather Service documentation; these should be rigorously applied, especially in vulnerable areas. Additional criteria/procedures proposed by the pane! (described in Chap- ter 4, under "Assessment Criteria and Procedures") should be followed in assessing the degradation of service and determining corrective actions. These assessment processes should be incorporated into official National Weather Service guidelines and procedures and used in conjunction with the requirements in P.I~. 102-567. The National Oceanic and Atmospheric Administration should take immediate steps to ensure that the 15 NEXRADs under the control of the Department of Defense, which are needed to avoid degraded coverage, function as fully committed elements of the national weather radar network, operating with the same standards, quality, and availability as the National Weather Service-operated NEXRADs. 4. The National Weather Service should ensure that maintenance for, operation of, and communication with NEXRADs that are not located near a Weather Forecast Office are in full accordance with network standards. In addition, responsibilities for weather services to the area covered by these NEXRADs should be unambiguously assigned to a specific Weather Forecast Office to ensure high-quality weaker services for that area. Staffing and communications capability should be commensurate with each Weather Forecast Off~ce's service area's responsibilities. 5. The storm-detection and warning performance of the composite national weather system, as a function of range from a NEXRAD, should receive an in-depth independent technical assessment that considers region-specific issues. This assessment should evaluate the warnings and reported events on a per-unit-area basis, as well as the traditional National Weather Service verification statistics. The assessment should include further testing in the Modernization and Associated Restructuring Demonstration in addition to tests at diverse geographic locations. 6. The adequacy of NEXRAD coverage with respect to He "no degradation of service" requirement should be reexamined in an independent study after all National Weather Service NEXRADs are commissioned.